SALIVARY GLAND IMAGING• Diagnostic imaging of salivary gland disease may be

undertaken to differentiate inflammatory processes from neoplastic disease, distinguish diffuse disease from focal suppurative disease, identify and localize sialoliths, and demonstrate ductal morphology.

• In addition, diagnostic imaging attempts to determine the anatomic location of a tumor, differentiate benign from malignant disease, demonstrate the relationship between a mass and adjacent anatomic structures, and aid in the selection of biopsy site.

• A number of imaging techniques are useful in the evaluation of the salivary glands.

ALGORITHM FOR DIAGNOSTIC IMAGING

• Plain film radiography is typically the appropriate starting point for imaging the major salivary glands from a cost- benefit point of view.– It can demonstrate sialoliths and the possible involvement of

adjacent osseous structures.• Because obstructive and associated unflammatory conditions

are the most common disorders and primarily involve the ductal system, conventional sialography is the most appropriate imaging modality.

• If the patient is allergic to the iodine contrast agent used in sialography, magnetic resonance imaging(MRI), computed tomography (CT) or ultrasonography (US) may be selected as an alternative imaging modality.

• Recent studies comparing the diagnostic yield of MRI with sialography suggest that MRI might replace sialography in the future as the imaging modality of choice for ductal pathosis.

• Sialography or CT is the best imaging modality for the detection of sialoliths(sialolithiasis). If sialography eliminates inflammatory disorders or suggests the presence of a space- occupying mass(either cystic or solid), then contrast enhanced(CT) or MRI is appropriate for evaluation.

• US is an alternative technique to differentiate cystic lesions from solid masses, as well as for identifying advanced autoimmune lesions.

• Functional disorders such as xerostomia are appropriately imaged with sialography or scintigraphy.

Salivary Gland Imaging Modalities: Indications, Advantages, and Disadvantages

Imaging Modality

Indications Advantages Disadvantages

Ultrasonography Biopsy guidance; mass detection

Noninvasive; cost-effective

No quantification of function; observer variability;limited visibility of deeper portions of gland; nomorphologic information

Sialography Stone, stricture; R/O autoimmune or radiation-induced sialadenitis

Visualizes ductal anatomy/ blockage

Invasive; requires iodine dye; no quantification

Radionuclide imaging

R/O autoimmune sialadenitis; sialosis, tumor

Quantification of function

Radiation exposure; no morphologic information

Imaging Modality Indications Advantages Disadvantages

Computed tomography

R/O calcified structure; tumor

Differentiates osseous structures from soft tissue

No quantification; contrast dye injection; radiation exposure

Magnetic resonance imaging

R/O soft-tissue lesion

Soft-tissue resolution excellent, with ability to differentiate osseous structures from soft tissue;no radiation burden

Dental scatter; contraindicated with pacemaker or metal implant; no quantification

Contd.

Plain-Film Radiography.

• Plain film radiography is a fundamental part of the examination of the salivary glands and may preclude the use of more sophisticated and expensive imaging techniques.

• It has the potential to identify unrelated pathoses in the area of the salivary glands that may be mistakenly identified as salivary gland disease, such as resorptive or osteoblastic changes in adjacent bone causing periauricular swelling mimicking a parotid tumor.

• Panoramic and conventional posteroanterior (PA) skull radiographs may demonstrate bony lesions, thus eliminating salivary pathosis from the differntial diagnosis.

• A plain film radiograph may demonstrate a deep antegonial notch, overdeveloped mandibular angle, and exostosis on the outer surface of the angle in cases of masseter hypertrophy.

• Plain film radiographs are useful when the clinical impression, supported by a compatible history, suggests the presence of sialoliths(stones or calculi).

• Such an examination should include both intraoral and extraoral images to demonstrated the entire region of the gland.

• Several sialoliths may be present at various locations. It is expedient to use about half the usual exposure to avoid overexposure of the sialoliths.

• However, this technique is limited by the fact that 20% of the sialoliths of the submandibular gland and 40% of those of the parotid gland are not well calcified and therefore are radiolucent and not visible in plain films. Radiolucent sialoliths are rarely found in the sublingual glands.

INTRAORAL RADIOGRAPHY

• Sialoliths in the anterior two thirds of the submandibular duct are typically imaged with a cross-sectional mandibular occlusal projection.

• The posterior part of the duct is demonstrated with a posterior oblique view, wherein the head of the patient is tilted back and maximally inclined toward the unaffected side.

• The central ray is directed parallel with the mandible in the area of the submandibular fossa and into the posterior part of the floor of the mouth.

Periapical radiograph showing sialolith

Occlusal radiograph demonstrating radiopaque stone in wharton’s duct

This roentgenogram occlusal view demonstrates a calcified

deposit in Wharton’s duct.

• Parotid sialoliths are more difficult to demonstrate than the submandibular variety as a result of the tortuous course of stensen’s duct around the anterior border of the masseter and through the buccinator muscle.

• As a rule, only sialoliths in the anterior part of the duct, anterior to masseter muscle, can be imaged on an intraoral film.

• To demonstrate sialoliths in the anterior part of the duct, an intraoral film packet is held with a hemostat inside the cheek, as high as possible in the buccal sulcus and over the parotid papilla. The central ray is directed perpendicular to the center of the film.

EXTRAORAL RADIOGRAPHY• A panoramic projection frequently demonstrates

sialoliths in the posterior duct or reveals intraglandular sialoliths in the submandibular gland if they are within the image layer.

• The image of most parotid sialoliths is superimposed over the ramus and body of the mandible, making lateral radiographs of limited value.

• To demonstrate sialoliths in the submandibular gland, the lateral projection is modified by opening the mouth, extending the chin, and depressing the tongue with the index finger. This improves the image of the sialolith by moving it inferior to the mandibular border.

• Sialoliths in the distal portion of stensen duct or in the parotid gland are difficult to demonstrate by intraoral or lateral extraoral views.

• However, a PA skull projection with the cheeks puffed out may move the image of the sialolith free of the bone, rendering it visible on the projected image.

• This technique may also demonstrate interglandular sialoliths that may be obscured during sialography.

• Less mineralized sialoliths may be obscured by the radiopaque soft tissue shadow in the PA skull view.

• Sialography

• Sialography is the radiographic visualization of the salivary gland following retrograde instillation of soluble contrast material into the ducts before imaging with plain films, fluoroscopy, panoramic radiography, conventional tomography, or CT.

• Sialography is one of the oldest imaging procedures and was first mentioned by Carpy in 1902. In 1925, Barsony and Uslenghi separately described sialography as a diagnostic tool.

• Sialography is the recommended method for evaluating intrinsic and acquired abnormalities of the ductal system because it provides the clearest visualization of the branching ducts and acinar end-pieces.

• Arcelin in 1913 was the first to present a complete roentgenographic demonstration of the human salivary gland, and also demonstrate a sialolith in Wharton’s duct following a bismuth injection.

• In 1925, Barsony utilizing a potassium iodide solution, demonstrated dilatation of Stensen’s duct. Later other people also contributed, and major advances for the procedure were proposed by Rubin, Holt and Blatt.

• Sialography can be performed on both the submandibular and parotid glands.

• Initial plain-film radiography is recommended for visualizing radiopaque stones and potential bony destruction from malignant lesions, as well as for providing a background for interpreting the sialogram.

Indications 1. Detection of a calculus or calculi or foreign bodies, whether

these are radiopaque or radiolucent.2. Determination of the extent of destruction of the gland,

secondary to obstructing calculi or foreign bodies.3. Detection and portrayal of fistulae, diverticula or strictures.4. Detection and diagnosis of the recurrent swellings and

inflammatory processes.5. Demonstration of a tumor and the determination of its

location, size and origin.6. Selection of site for biopsy.7. Outline of the plane of the facial nerve as a guide in planning

a biopsy or detection.8. Detection of residual stone or stones, residual tumor, fistula

or stenosis or retention cysts following prior simple lithotomy or other surgical procedures.

• Sialography has also been recognized as a therapreutic procedure because the dialatation of the ductal system produced during the study may aid in the drainage of ductal debris.

• Also, iodine which is used as a contrast media has beneficial antiseptic properites.

Contraindications• Patients with a known sensitivity to iodine compounds, and

patients who have experienced severe asthmatic attacks or anaphylaxis following use of iodine compounds in a prior radiologic examination should not be considered subjects for this technique. ( A history of nausea and vomiting following the intravenous injection of contrast media is not considered a contraindication.)

Note: The amount of contrast media employed is relatively small and the route of administration is ductal rather than venous.

• The use of sialography during the period of acute inflammation of the salivary system is contraindicated.

During this period the ductal epithelium may be disrupted and escape of the contast medium from the ductal system into the parenchyma can produce severe foreign bodies reaction accompanied by severe pain. This is especially true when oily contrast medium is used.

• The adminstration and retention of the iodinated contrast material may interfere with subsequent thyroid function tests.

CONTRAST MEDIA 1. The ideal contrast medium for the study of salivary ductal

system has not as yet been devised. An ideal sialographic contrast medium should have the following characteristics:

2. Physiologic properties similar to those of saliva.3. Miscibility with saliva.4. Absence of local or systemic toxicity.5. Pharmacological inertness.6. Satisfactory opacification.7. Low surface tension and low viscosity to allow filling of the

fine components of the ductal system.8. Easy elimination, but duarable enough to permit time for

satisfactory radiographs.9. Residual contrast media should be observed by the salivary

glands and detoxified by the liver or excreted by the kidney.

• Two types of contrast media are presently available for contrast studies of the salivary ducatal system-

– Water soluble – Oil based.

Water soluble media• The majority of investigators actively participating in

sialographic studies at this time prefer the use of water soluble media, which are principally iodinated benezene or pyridone derivatives.

• These compounds have a lower viscosity and a lower surface tension than oil based media and are relatively more miscible with the salivary secretions.

• These physical characteristics permit filling of the finer ductal system under lower pressure and facilitate prompt drainage.

• Ductal injection using a water soluble medium is accompanied by little pain or discomfort, and no significant granulomatous has been reported yet.

• The residual contrast medium in the ductal system i.e., that amount remaining after drainage through the ductal orifice, is absorbed and excreted through the kidneys.

• Because of its miscibility with saliva, a water soluble contrast medium is considered more physiologic and represents a better medium for evaluating the function of the salivary gland.

• Suzuki has expressed the belief that the water soluble media can coat and outline the calculi more adequately then oil based media.

• The following water soluble media have been utilized in sialography.– Hypaque 50%– Hypaque M 75%– Renografin-60 and -76– Sinografin– Isopaque– Triosil– Dionosil– Diodrast.

• Hypaque and Renografin are the water soluble media of choice.

Fat soluble media• There are two types of fat soluble contrast media-• Iodized oil (e.g., Ethiodol-ethiodized poppyseed oil)• Water insoluble organic iodine compounds(e.g., Lipiodol

– iodized poppy seed oil and Iodochloral – choriodized peanut oil).

• The fat soluble contrast media, on the whole, produce a satisfactory degree of radiographic opacification.

• These media are excellent contrast agents if the ductal system under examination are intact.

• If the ductal epithelium is damaged, the extravasation of the fat soluble contrast media can produce severe foreign body reactions with focal necrosis of the parenchyma and stroma and an accompanying obliteration of the adjacent ducts.

• The fat soluble media are more viscous and require a higher injection pressure than do the water soluble media to visualize the finer ductules.

• Moreover, once the finer ductules are filled, the oil based media are poorly eliminated and may cause ductal obstruction. The principal avenue of elimination of fat soluble media from the ductal system is by way of the ductal orifice, and the ductal diameters are occaisonally distorted because higher pressure is needed for injection.

• When this type of agent is used, any calculus encountered in the duct may be displaced backward, the ductal epithelium may occasionally be damaged, and the injection is usually accompanied by a greater degree of discomfort.

• The one fat soluble medium which now enjoys unique exception to the disadvantages noted here is Ethiodol. Ethiodol is more fluid than the other oil based media. Hence Ethiodol is the sialographic contrast medium of choice if a fat soluble iodine contrast agent is desired.

Procedure

• All sialographic techniques can be divided into three phases:

1. Preliminary plain film evaluation2. The injection or filling phase3. The parenchymal phase (if water soluble is used)

or evacuation phase (when fat soluble is used).

Equipment

• Essential equipment consists of lemon juice, cannula, syringe, cotton swab, tongue depressor, tenner lacrimal dialators(cannula), contrast medium.

• Cannulae : The larger cannula is for the parotid duct. It has two side holes and blunt tip which serves both as a probe and a cannula. Its larger proxinal end will act as a plug to prevent backflow of contrast medium through the ductal orifice. The smaller cannula with an end hole is designed for the smaller orifice of the submandibular duct.

Catheter

• Preliminary films are obtained to evaluate possible bony erosion of the mandible, calcifications, mass densties (particularly when parapharyngeal in location), and radiopaque calculi.

• Films are taken with a slightly lower kilovoltage than routine mandibular views to allow better visualization of the paramandibular soft tissues.

• After the preliminary films have been reviewed, the duct orifice is directly visualized. The parotid orifice is adjacent to the upper second molar tooth, and the submandibular orifice is adjacent to the frenulum of the tongue on a small papilla on the floor of the mouth.

• Palpation of the gland on allowing the patient to suck a lemon is often necessary to identify the point of salivary efflux.

• The orifice is then gently dilated with a standard blunted, double-ended dilator with special cane to preserve the comfort of the patient and avoid mechanic rupture of the duct.

• A piece of sterile gauze is placed between the cannulated orifice and the tongue. The patient is requested to stabilize the tubing with gentle pressure of the tongue laterally, holding mouth and lips in a closed position around the tubing which is taped to the skin out of the radiographic field. For contrast material we use Ethiodol on Renografin-60 or -76.

• Ethiodol provides greater density of the ducts and parenchyma.

• If extravasation is likely to occur, such as in large ductal stones, strictures, and traumatic cannulation water soluble contrast material such as Renografin is the preferred contrast agent.

• Also, since Ethiodol remains in tissues and cavities for many months and may lead to granuloma formation, cases in which cavitation is suspected within glands should be performed with a water soluble agent.

• When the patient is comfortable, the contrast media is gently injected.

Preparation of the patient and radiographic technique

• The filming procedure is carried out with the patient in the supine position. All dentures should be removed. Three to four sets of films are obtained during the entire procedure. These sets consists of :

1. Preliminary films in the anteroposterior, lateral, and oblique positions.

2. Filling phase films in the anteroposterior, lateral and oblique positions. These films should be completed under image amplification control. Serial spot films should be obtained showing the gland in different profiles.

3. The postevacuation phase following stimulation of saliva folw consists of films completed 5 minutes after the emptying phase in the anteroposterior, lateral and

– Oblique positions. Should these films demonstrate retention of contrast media, films may be made at 1 hour and 24 hours after these studies.

• For the straight anteroposterior view, the chin is flexed on the neck and the central ray is directed immediately below the mouth.

• For the oblique views the x-ray is angulated approximately 25 degrees toward the head.

• For the studies of submandibular gland, the lateral view should be obtained with the neck hyperextended so that the submandibular gland is projected below the mandible.

• In obtaining views of the sublingual glands, the floor of the mouth may be depressed with a cotton pad under the tongue on the affected side. This maneuver will displace any sublingual calculus from the mandible and aid in depicting the calculus on the film.

Radiograph during sialography

• Additional views are desirable to portray special features of the salivary ductal system more adequately. For example:

– Reverse basilar view to demonstrate the deep portion of the parotid gland.– A film made with the cheek in the blow out position in the anteroposterior

view to demonstrate the superficial portion and the course of stensen’s duct of parotid gland.

– Occlusal view to demonstrate the distal submandibular wharton’s duct.– Filming of the filling phase with the mouth open will reduce

superimposition of the mandible on the parotid gland.– Sterioscopic studies are invaluable for the study of the spatial relationships

of the gland and the duct.– Subtraction views are of great value in the delineation of the finer ducts

and of the sublingual ductal system.– Plesioradiography is a technique in which small x-ray tube is placed in

contact with the facial soft tissues contralateral to the gland being examined in an attempt to eliminate the obscuring overlying bony structures.

• The amount of contrast material injected should be governed by the production of pain.

• Following the procedure, the patient should be encouraged to massage the gland and/or to suck on lemon drops to promote the flow of saliva and contrast material out of the gland.

• Postprocedure radiography is done approximately 1 hour later. If a substantial amount of contrast material remains in the salivary gland at that time, follow-up visits should be scheduled until the contrast material empties or is fully resorbed.

• Incomplete clearing can be due to obstruction of salivary outflow, extraductal or extravasated contrast, collection of contrast material in abscess cavities, or impaired secretory function.

• The normal ductal architecture has a “leafless tree” appearance.

• As the ductal structure branches through the major glands, the submandibular gland demonstrates a more abrupt transition in ductal diameter whereas the parotid gland demonstrates a gradual decrease in ductal diameter.

• Ductal stricture, obstruction, dilatation, ductal ruptures, and stones can be visualized by sialography.

• Nonopaque sialoliths appear as voids. Sialectasis is the appearance of focal collections of contrast medium within the gland, seen in cases of sialadenitis and Sjögren’s syndrome.

• The progression of severity is classified as punctate, globular, and cavitary. Sialography is the imaging technique of choice for delineating ductal anatomy and for identifying and localizing sialoliths.

• It also may be a valuable tool in presurgical planning prior to the removal of salivary masses.

Retrograde Sialogram – Lateral view

• Interventional sialography.

– MR sialography

Roentgenographic interpretation• Parotid gland: – The parotid gland consists of two portions, the

superficial and the deep. The two portions are connected by an isthmus in which ducts are normally seen stretched, an appearance which should not be mistaken for a pathologic finding.

– Stensen’s duct is about 6.0 cm in length and 1.0 to 3.0 mm in width and it passes forward and lateral to the masseter muscle. At its anterior border the duct pierces the buccinator muscle and the mucous membrane of the mouth and opens on the mucosal surface of the cheek opposite the upper second molar teeth.

Lateral film of parotid gland without definite abnormality

Anteroposterior view also reveals no definitelesion.

• Submandibular gland: – The submandibular gland is situated in the submandibular triangle of

the neck. The duct of the submandibular gland, wharton’s duct, is about 5.0 cm. Its lumen is appoximately 2.0 to 4.0 mm in width, wider than the parotid duct. Its orifice, however, is narrower and is situated on the summit of a small papilla at the side of the lingual frenum, at the sublingual salivary papilla. Also the walls of the submandibular duct are much thinner than those of the parotid duct and can be easily injured during manipulation, if a long rigid cannula is utilized.

• Sublingual gland:– The sublingual gland is separated anteriorly from the submandibular

gland by the mylohyoid muscle. It is almond shaped and is situated beneath the mucous membrane of the floor of the mouth.

– It has 8-20 excretory ducts, which open separately into the mouth superior to wharton’s duct on the crest of the mucous membrane known as plica sublingualis. Cannulation the sublingual orifices is virtually impossible. However, when the major sublingual ducts empty into Wharton’s duct, concomittant sublingual sialography is obtained on occasion during the visualization of the submandibular gland.

Acinar filling

• Occasionally acinoparenchymal filling is seen after injection of contrast media into a main duct.

• Ollerenshaw indicated that acinar filling is a normal event, and nonfilling of the acini, on the other hand would indicate incomplete filling or abnormal acini with debris contained in the acini.

• Concluding that, filling or nonfilling of the acinar parenchyma does not constitute a pathologic finding by itself.

• Approximately 400mm of mercury pressure is required to fill the normal parotid acini with oil contrast media, according to Ollerenshaw.

• The submandibular acini are more rapidly filled than those of the parotid gland. Possible reasons for this can be:

1. The submandibular acini are larger.2. The wall of submandibular duct is thinner and offers

less resistance.3. The second and third order ductules are short, making

the acini more accessible to the contrast media.

• The main parotid duct, on the other hand has a thicker fibrous wall and offers more resistance to injection.

SIALOLITHIASIS

• Sialolithiasis is the formation of a calcified obstruction within the salivary gland.

• Radiopaque stones situated in the submandibular ducts may be best demonstrated by utilizing occlusal views. Radiopaque calculi in the parotid duct may be shown to best advantage by employing a cheek blow out anteroposterior view and an open mouth lateral.

• Stones may be mobile, moving with the pressure and flow of contrast media, or they may be fixed and obstructive in character, delaying the filling as well as the emptying of the contrast media from the ducts.

• Water soluble contrast media will coat stones and outline the ductal systems better than fat soluble media.

• If the stones are large enough they will, on occasion, erode the ductal epithelium and create a pseudodiverticulum. When obstruction of a salivary duct occurs, continuous secretion of the salivary gland will produce distension and increase in the pressure in the alveoli and ductal system, which finally leads to progressive pressure atrophy of the parenchyma.

• When salivary flow is obstructed, stasis and infection can result. These in turn may lead to sialodochitis, sialadenitis, abscess, or fistula.

• The importance of sialography lies also in the fact that the investigation may be repeated after treatment to confirm that the calculi have been removed.

• Radiopaque stones may be distinguished from osteomas. The more dense osteomas lack lamination and are visibly contained within the structure of the mandible in both the anteroposterior and lateral views.

This is a sialogram of the submandibular gland demonstratingan uncalcified sialolithiasis in Wharton’s duct, which can be

visualized where the submandibular duct overlies the inferior alveolar canal.

Sialodochitis

• Sialodochitis is an inflammation of the ductal system of the salivary gland.

• Plain film studies may demonstrate soft tissue swelling. In the filling phase of the sialogram, fusiform dilations of the ducts with or with out tortuosity of the ductal system may be seen.

• In more advanced cases, contrast studies may demonstrate segmental stricture and dilation of the larger ducts.

• In contrast to the appearance seen in sialadenitis, the acini and the terminal ductules are not dilated.

• In the emptying phase elimination of the contrast media is usually delayed.

• Sialodochitis may be difficult to distinguish from glands containing salivary calculi, since this condition also results in segmental dilatation of the ducts with associated atrophic acini.

Sialadenitis

• Sialadenitis is the inflammation of the parenchyma of the salivary gland.

• In the plain film study of this entity, soft tissue swelling is seen in the gland.

• In the filling phase, the sialogram shows phase, the sialogram shows saccular dilatation of the acini and terminal ducts, thus differentiating it from sialodochitis, in which the acini and terminal ductules are not dilated.

• In the emptying phase, elimination of the contast media is also delayed.

Chronic sialadenitis

• The pathologic changes associated with these conditions usually result in dilatation of the acini and the ductal system.

• There are lymphocytic, plasma cell, or macrophage infiltrates surrounding the ductal system. The ductal epithelium is denerative in character.

Chronic sialadenitis: Parotid sialogram demonstrating ductal dialatation to an area of obstruction.

Salivary tumors

• Salivary tumors are uncommon. Of those that occur, 95.4% are parenchymal in origin and 4.6% are interstitial in character.

• Interstitial tumors arise from the vessels, lymph nodes, and nerves.

• Parenchymal tumors can be benign, malignant, or potentially malignant.

• Sialography aids in the determination of the size of the tumor, its location, its origin( whether intrinsic or extinsic), the presence of glandular impairment of the adjacent tissues.

• Benign lesions are usually more circumscibed and may be encapsulated, in appearance, whereas malignant lesions are usually infiltrationg in character.

Circumscribed or encapsulated lesons

• The circumscribed lesions which are demonstrated by sialographic studies may be centrally or peripherally located.

• Centrally located lesions can be parenchymal or interstitial in origin, while the peripheral lesions can be intrinsic or extrinsic to the gland.

• Large lesions are located easily than the smaller lesions.

Central solid lesions

• Centrally located lesions have a characteristic ball in hand appearance when a defect is located within the gland.

• The sialogram shows the adjacent ducts draped and stretched around the mass.

• Plain film studies show enlargement of the gland.• During the filling phase of the sialogram in the study of central

parenchymal lesions, a mass effect is seen in the center with the adjacent ductal system displaced and stretched around it.

• The mass may appear nodular and the displaced ductal system may seem sharply angulated.

• Because some of the glandular tissue is involved by the mass, there is a decrease in salivary function, and elimination of the contrast material in the emptying phase appears delayed.

• Central interstitial lesions such as angiomas, enlarged lymph nodes, or neuromas are located in the interstitium rather than in the glandular parenchyma.

• Unlike, the parenchymal lesion, the ductal system in interstitial lesions is smoother in appearance.

• Because the glandular tissue is displaced rather than destroyed, there is no significant compromise of the salivary function.

Peripheral solid lesions

• During the filling phase intrinsic lesions will cause mechanical displacement of the adjacent ductal system.

• This displacement is characterized by an angulation which is sharper than that found in an extrinsic lesion.

• Extrinsic lesions of the salivary gland can also cause mechanical displacement of the adjacent ductal system, but in these cases the ductal system is seen to be smoothly stretched, unlike the sharp angulation found in intrinsic lesion.

Circumscribed cystic lesions

• The pressure within a cystic lesion is usually evenly distributed on its surface. Thus, a cystic lesion, whether peripherally or centrally located, is more globular in appearance than other types of lesions.

• The ductal system is displaced and is smooth and spherical in appearance rather than nodular as in the case of solid lesions.

• Ultrasound echography is most helpful in differentiating a cystic lesion from a solid tumor. Cystic lesions are echo free, whereas solid tumors are echo- reflecting.

• Radioisotope scans may also be employed in differentiating space-occupying lesions. Since both cysts and carcinomas have replaced the normal glandular tissue, they will show as areas of nonopacity, while benign mixed tumors and warthin’s tumors will show varying degrees of radioactivity.

Lateral tomographic section of opacifiedparenchyma of parotid gland revealing slightly irregularfilling defect, in superior portion. Histologic examinationrevealed Warthin’s tumor (adenolymphoma).

Infiltrating lesions

• Sialograms of infiltating lesions are characterized by disruption of the normal glandular architecture.

• Glandular tissue may be destroyed and ductal system may be altered.

• A bizarre irregular pattern should arouse suspicion of an infiltrating malignant lesions.

• However it should be differentiated from an inflammatory process accompanied by destruction of the glandular tissue.

• In an inflammatory process the lesion is usually diffuse and not uncommonly bilateral.

• In the infiltrating tumor, on the other hand the destruction may be localized within the gland and normal glandular tissue may also be found in the gland.

Autoimmune disease-Sjogren’s syndrome and Mikulicz’s disease.

• Mikulicz’s disease is clinically described as a benign, asymptomatic, symmetrical enlargement of the lacrimal and salivary glands.

• Sjogren’s syndrome is classically described as decreased or absent lacrimation associated with a keratoconjunctivitis sicca, rhinostomato-pharyngolaryngitis sicca, and enlargement of the parotid glands and chronic polyarthritis.

Sjogren’s syndrome: Parotid sialogram demonstrating atrophy and punctate sialectasia

• With the advent of lymphoid infiltrates in the salivary gland, the acini become progressively more separate and atrophic.

• Fragmentation and disintegration of these structures then occur, causing them and the terminal ductules to appear dilated.

• In more advanced cases, further disintegration of the acini and coleasance of small puddles of contrast media occur.

Trauma

• The salivary gland may sustain trauma, usually from automobile accidents or gunshot or stab wounds.

• The most common findings incases of trauma include displacement of the glands and ducts by adjacent hematoma, occlusion of the main duct or ductules in the later stages because of scarring, and the creation of a cavity into which saliva and contast media may empty, thus producing a sialocele.

Post irradiation changes

• The salivary glands are frequently damaged in the process of therapuetic irradiation of a carcinoma of the oral cavity.

• There is a wide variation in the radiosensitivity of the salivary glands.

• During the early phase, there is an acute swelling of the salivary glands caused by interstitial edema or duct obstruction or both.

• A few days later both the parencyma and the size of the gland are noticeably decreased.

• One month after cancericidal doses, massive degenration con often be seen continuing for about 3 months.

• Four or more months after cancerididal doses of radiation, the late changes occur. There is patchy distortion of nearly all acini with a few serous acini remaining.

• Fibrosis surrounds the ducts, lobules and acini.

Submandibular sialography in combination with pneumoradiography and tomography

• A procedure combining sialography and pneumoradiography and tomography has been devised and utilized by Granone et al. for the visualization of the submandibular periglandular space.

• In this procedure, submandibular sialography is performed first: carbon dioxide is then introduced into the periglandular space by intraoral, mylohyoid, or transcutaneous puncture.

• Tomographic sections of the gland are then obtained to visualize the opacified portion of the periglandular space.

• Utilizing this procedure, satisfactory definition of the submandibular space is obtained, as well as definition of any infiltration arising in the gland itself or from the adjacent tissues.

Ultrasonography.• Ultrasonic techniques applied to diagnosis of diseases of

the salivary glands involve the transmission of energy into the salivary tissues, receiving that energy after it has been reflected by the tissues, and recording it so that it can be presented for our interpretation.

• When one considers that the majority of structures and associated pathology in the neck lie only between one to five centimeters below the skin surface, and given the superior resolution that high resolution US can attain, it is not surprising that US is gaining popularity in the field of head and neck imaging.

• As it is relatively inexpensive and is readily available, the use of US will continue to increase.

• Ultrasonic diagnostic equipment consists of a transducer, which is capable of converting electrical energy into mechanical vibrations called ultrasound.

• A linear 7.5 – 10MHz probe with a relatively small footprint i.e. a small contact surface area is optimal. Higher frequency probes i.e. 10 MHz and above, allow superior resolution.

• An understanding of the anatomy of the region is the key to the radiological approach.

• Traditionally the neck is divided into triangles based on muscular landmarks and boundaries.

• Knowledge of the anatomy of just three muscles- the sternocleidomastoid, digastric and omohyoid- forms the basis to understanding the triangles of the neck.

• The sternocleidomastoid, which runs from the mastiod process to the clavicle and sternum, divides the neck into two large triangles: anterior and posterior.

• The anterior triangle is subdivided into supra and infra- hyoid portions. The suprahyoid portion is further divided by the anterior belly of diagastric muscle into the submental and submandibular triangles. The infrahyoid portion is divided by the superior belly of the omohyoid muscle into muscular and carotid triangles. The posterior belly of digastric marks the superior border of the carotid triangle.

• The posterior triangle is demarcated by the posterior border of sternomastoid anteriorly and the anterior border of trapezius posteriorly.

• The apex is formed by the occiput while the base of the triangle is formed by the clavicle. The triangle is further subdivided by the posterior belly of the omohyoid muscle, forming an occipital traingle superiorly and a supraclavicular triangle inferiorly.

• It is important to remember that there is no septum or fascial plane that physically separates the anterior from the posterior triangle.

• Due to their superficial locations, the parotid and submandibular glands are easily visualized by ultrasonography although the deep portion of the parotid gland is difficult to visualize because the mandibular ramus lies over the deep lobe.

• Ultrasonography is best at differentiating between intra- and extraglandular masses as well as between cystic and solid lesions. In general, solid benign lesions present as well-circumscribed hypoechoic intraglandular masses.

• Ultrasonography can demonstrate the presence of an abscess in an acutely inflamed gland, as well as the presence of sialoliths, which appear as echogenic densities that exhibit acoustic shadowing.

Salivary gland technique

1. The scan plane is maily transverse(axial) with oblique or longitudinal adjustments to confirm vessels and to help localize them.

2. Have the patient sit or recline with the neck extended.

3. Always scan both sides for symmetry and to exclude further clinically nonpalpable lesions as there is a risk of bilateral disease.

4. Scan all nodal territories.

Ultrasound anatomy of the parotid space

1. Homogenous, hyperechoic gland.2. Stensen’s duct- bright parallel echogenic lines, no more than

3 mm in diameter. Normally not seen beyond the parenchyma.

3. Intraglandular ducts- short discrete hyperechoic thin lines within the gland parenchyma.

4. Retromandibular vein- running obliquely through the gland as a well defined hypoechoic tube. Landmark for facial nerve.

5. External caritid artery is deep and parallel to the vein.6. Posterior belly of digastric- demarcates carotid space

boundary.7. Intraparotid lymph nodes- round/oval<5mm diameter,

echogenic hilus. Commonly lie in superficial lobe but may also be seen in the deep lobe.

Axial image of body of parotid

Axial image of parotid tail

Ultrasound anatomy of submandibular and sublingual spaces.

1. Homogenous hyperechogenecity similar to the parotid glands. The sublingual glands demonstrate similar echogenecity to the outer salivary glands.

2. Wharton’s duct- this is seen when it is abnormally dilated, but it may occasionally be seen in normal cases. The duct extends from the gland hilus medially to curve around the mylohyoid muscle, appearing lateral to the hyoglossus muscle. It then advances medially to the papilla in the floor of the mouth.

3. The intraglandular ducts appear as in the parotid, i.e. short, defined hyperechoic lines.

Sagittal images of submental region

4. The anterior division of the retromandibular vein is sandwiched between the posterior pole of the submandibular gland and the antero-inferior margin of the parotid gland. This landmark may be important when it is displaced by a large mass, giving a further indication as to the origin of the lesion, i.e. parotid or submandibular.

5. The sublingual glands are easily visualized submentally deep to the mylohyoid and lateral to the geniohyoid/ genioglossus.

Tranverse region of submandibular region

Coronal region of submandibular gland showing superficial and deep region

Ultrasound appearances in acute inflammation.

1. Sialadenitis- hetrogenous, hypoechoic gland, micro- abscesses.

2. Inflammatory mass- hypoechoic, ill- defined gland, ducts within lesion.

3. Abscess- frank, fluid, gas microbubbles.

ill-defined abscess

Chronic sialadenitis

Submandibular mass in patient of Sjogren's syndrome

Ultrasonography of a pleomorphic adenoma of the poleof the parotid gland, showing a lobular shape, homogeneous

internal echoes,and enhanced posterior echoes

• Makula and colleagues studied a group of patients with Sjögren’s syndrome and reported the appearance of parenchymal inhomogeneity.

• They also noted good agreement between ultrasonographic, sialographic, and scintigraphic results in this patient group.

• Ultrasonography is a noninvasive and cost-effective imaging modality that can be used in the evaluation of masses occurring in the submandibular gland and the superficial lobe of the parotid gland.

• Radionuclide Salivary Imaging

• Scintigraphy with technetium (Tc) 99m pertechnetate is a dynamic and minimally invasive diagnostic test to assess salivary gland function and to determine abnormalities in gland uptake and excretion.

• Radioisotope scans or the salivary glands may be desirable for two reasons:1. To study the morphology of the glands and any space occupying

lesions.2. To evaluate the salivary function of the glands.

• The Principal limitation of the radioisotope scan is resolution, or lack of detail. Present instrumentation cannot evaluate any tumor less than 1.0 to 2.0 cm in diameter.

• Technetium is a pure gamma ray–emitting radionuclide that is taken up by the salivary glands (following intravenous injection), transported through the glands, and then secreted into the oral cavity.

• Uptake of Tc 99m by a salivary gland indicates that there is functional epithelial tissue present.

• The Tc-99m scan can be used as a measure of secretory function as it has been shown to correlate well with salivary output.

• Tc 99m is capable of substituting for chloride (Cl–) in the sodium-potasium (Na+/K+)/2Cl– salivary transport pump and serves as a measurement of fluid movement in the salivary acinar glands.

• Scintigraphy is indicated for the evaluation of patients when sialography is contraindicated or cannot be performed (such as in cases of acute gland infection or iodine allergy) or when the major duct cannot be cannulated successfully.

• It has also been used to aid in the diagnosis of ductal obstruction, sialolithiasis, gland aplasia, Bell’s palsy and Sjögren’s syndrome.

• Salivary imaging is performed following the injection of 10 to 20 mCi of Tc 99m pertechnetate.

• The uptake, concentration, and excretion of the pertechnetate anion by the major salivary glands and other organs is imaged with a gamma detector that records both the number and the location of gamma particles released in a given field during a period of time.

• This information can be stored in a computer for later analysis or recorded directly on film from the gamm detector, to give static images.

• Several rating scales exist for the evaluation of salivary scintiscans; however, no standard rating method presently exists.

• Current approaches to functional assessment include visual interpretation, time-activity curve analysis, and numeric indices.

• Most radiologists read Tc 99m scans by using visual interpretation and clinical judgment.

• Radionuclide imaging can provide information regarding salivary gland function by generating a time-activity curve.

• A normal time-activity curve has three phases: – flow, – concentration, and – washout.

• The flow phase is about 15 to 20 seconds in duration and represents the phase immediately following injection when the iostope is equilibrating in the blood and accumulating in the salivary gland at a submaximal rate

• The concentration phase represents the accumulation of Tc 99m pertechnetate in the gland through active transport. This phase starts about 1 minute after administration of the tracer and increases over the next 10 minutes.

• A normal image should demonstrate uptake of Tc 99m by both the parotid and submandibular glands, and the uptake should be symmetrical.

• The last phase is the excretory or washout phase. During this phase, the patient is given a lemon drop, or citric acid is applied to the tongue to stimulate secretion. Normal clearing of Tc 99m should be prompt, uniform, and symmetrical.

• Activity remaining in the salivary glands after stimulation is suggestive of obstruction, certain tumors, and inflammation.

Anteroposterior view scintigrams developed during sequentialsalivary scintigraphy of the parotid gland for a normal patient (top row)

and a patient with acute sialadenitis following administration of phenylbutazone

Interpretation

• Space occupying masses as delineated by radiopaque studies are classified as hot, warm, or cold lesions.

• Warthin’s tumor, which is thought to be derived from ductal epithelium incorporated I lymph nodes adjacent to or imbedded in the parotid gland, is the only tumor which will consistently show a “hot” lesion due to increased activity. Other tumors like oncocytoma also retain the tracer.

• Carcinomas like cysts, are thought to replace completely the normal glandular cells and appear as cold lesions of decreased activity.

• Most of the mixed tumors will appear as warm lesions with an uptake similar to that found in normal glandular tissue.

• Inflammatory lesions showed a general increase in the uptake of the isotope as in cases of acute staphylococcus parotitis and during the early stage of mumps because of hyperemia and edema.

• In late stage of mumps uptake of isotope decreases because of epithelial necrosis and lymphocytic infiltration of the interstitial tissue. In chronic recurrent parotitis there is a general decrease in the activity of the whole gland.

• Patients with Sjogren’s syndrome appear to have the lowest recorded uptake by the salivary glands.

Arteriography

• With the advent of selective arteriography, the ability to localize and selectively catheterize the arterial channels supplying the salivary gland stuctures has now become a reality.

• Utilization of this technique is important in the study of salivary tumors because it not only defines the vasculature of the tumor, but also delineates the origin of the vascular supply.

Computed Tomography and Magnetic Resonance Imaging.

• Computed tomography (CT) images are produced by radiographic beams that penetrate the tissues.

• Computerized analysis of the variance of absorption produces a reconstructed image of the area.

• Coronal and axial images are usually obtained. • The varying water content of tissues allows for magnetic

resonance imaging (MRI) to distinguish tissue types. Tissues absorb and then re-emit electromagnetic energy when exposed to a strong electromagnetic field. Analysis of the net magnetization by radiofrequency is reconstructed to provide an image. Images are described as T1- or T2-weighted images, according to the rate constant with which magnetic polarization or relaxation occurs.

• CT and MRI are useful for evaluating salivary

Contrast image CT at the level of the mandible showing submandibular gland.

• CT and MRI are useful for evaluating salivary gland pathology, adjacent structures, and the proximity of salivary lesions to the facial nerve. The retromandibular vein, carotid artery, and deep lymph nodes also can be noted on CT.

• Osseous erosions and sclerosis are better visualized by CT than by MRI. Since calcified structures are better visualized by CT, this modality is especially useful for the evaluation of inflammatory conditions that are associated with sialoliths.

• Abscesses have a characteristic hypervascular wall that is evident with CT imaging. CT also provides definition of cystic walls, making it possible to distinguish fluid-filled masses (ie, cyst) from abscess.

• CT images of salivary glands should be obtained by using continuous fine cuts through the involved gland.

• Non-enhanced and enhanced CT images are routinely obtained.

T1 wieghted image of suprahyoid neck demonstrating submandibular gland.

Ranula

• On CT ranulas are thin walled unilocular homogenous, cystic lesion.

• On MRI,ranulas are typically hypointense to skeletal muscle on T1 weighted images and isointense to cerebrospinal fluid on T2 weighted images.

• An imaging diagnosis of dividing ranula should be considered only when the lesion abuts or involves the sublingual space.

Axial contrast enhanced CT of ranula at the level of mandible demonstrates origin

Axial contrast enhanced CT of ranula at the level thyroid cartilage demonstrates unilocular cystic in the anterior triangle.

This is an axial view of a CT image soft tissue windowdemonstrating a tumor of the right parotid.

• Ultrafast CT and three-dimensional–image CT sialography have been reported by Szolar and colleagues to be an effective method of visualizing masses that are poorly defined on MRI; they also advocate ultrafast CT for patients who are unable to lie still long enough for adequate MRI (pediatric, geriatric, claustrophobic, and mentally or physically challenged patients) and for patients for whom MRI is contraindicated.

• The disadvantages of CT include radiation exposure, administration of intravenous iodine-containing contrast media for enhancement, and potential scatter from dental restorations.

• MRI has become the imaging modality of choice for preoperative evaluation of salivary gland tumors because of its excellent ability to differentiate soft tissues and its ability to provide multiplanar imaging.

• It provides images for evaluating salivary gland pathology, adjacent structures, and proximity to the facial nerve.

• In T1-weighted images, the normal parotid gland has greater intensity than muscle and lower intensity than fat or subcutaneous tissue.

• In T2-weighted images, the parotid has greater intensity than adjacent muscle and lower intensity than fat.

• Structures and conditions that are dark on both T1- and T2-weighted images include calcifications, rapid blood flow, and fibrous tissue.

MRI scan

• MRI is preferred for salivary gland imaging because– (a) patients are not exposed to radiation, – (b) no intravenous contrast media are required routinely,

and– (c) there is minimal artefact from dental restorations.

• MRI is contraindicated for patients with pacemakers or metallic implants such as aneurysmal bone clips.Patients who have difficulty maintaining a still position or patients with claustrophobia may have difficulty tolerating the MRI procedure, which may result in poor image quality.