Indian J Dent Adv 2012; 4(2) 868

Bilateral Masseter MuscleHypertrophy-a Case Report

and Review of LiteratureSujatha S Reddy1, Giridhar A G2, Ravleen Nagi3

ABSTRACT:

Masseter muscle hypertrophy is a rare condition characterized

by unilateral or bilateral enlargement of the masseter muscle

affecting both males and females following puberty. It usually

manifests in late adolescence or early adulthood. Its etiology

remains unknown. Masseter muscle hypertrophy produces facial

asymmetry and familiarity with this condition is important to

rule out other pathologies such as parotid gland tumors and

dental infection. Here in, reporting a case of bilateral masseteric

hypertrophy in a 55 year old female patient diagnosed using

imaging modalities such as conventional radiography,

ultrasonography and computed tomography.

Key words: Masseter muscle hypertrophy, facial asymmetry,

bone spur, ultrasonography, computed tomography

C A S E R E P O R T

doi: ...........................

1Professor3PG StudentDept. of Oral Medicine, Diagnosis and RadiologyM.S. Ramaiah Dental College & Hospital, MSRIT Post,New BEL Road, Bangalore-560054, Karnataka (India)

2Associate ProfessorDept. of RadiodiagnosisM.S. Ramaiah Dental College & Hospital, MSRIT Post,New BEL Road, Bangalore-560054, Karnataka (India)

Article Info:

Received: April 11, 2012;Review Completed: May, 10, 2012;Accepted: June 8, 2012Published Online: August, 2012 (www. nacd. in)© NAD, 2012 - All rights reserved

Email for correspondence:oralmedradiology@gmail.com

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INTRODUCTION

Masseter muscle hypertrophy (MMH) is a benign increase in the size of masseter muscle that may affectone or both sides of the face.1 MMH was first described by Legg in 1880.2 Although a few cases have beendocumented since then, it has been stated that this disorder is more common than generally recognized.Pain may be a symptom, but most frequently the clinician is consulted for cosmetic reasons. In few casesprominent exostoses at the angle of the mandible is noted.3 MMH is associated with variable causativefactors such as genetic predisposition, bruxism and clenching associated with psychological stress, anxiety,sleep disorder, malocclusion and temporomandibular disorders.4, 5 Zachariades et al reported two cases wherevascular lesion gradually subsided to a residual muscular hypertrophy.1 A congenital variant also exists, butacquired MMH is by far the most frequent. Most cases of MMH are bilateral and symmetric, but asymmetryis not unusual. Unilateral occurrence also can be observed when patients clench or chew primarily on oneside.6

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Indian J Dent Adv 2012; 4(2) 869

Diagnosis is based on the awareness of thecondition, clinical and radiographic findings andexclusion of other pathologies in the angle of thejaw such as parotid tumors, vascular tumors andlipoma.3 In MMH, a long standing uniform mass isnoted unlike the irregular and nodular growth thatcharacterizes other benign and malignantneoplasms. Panoramic radiographic examinationcomplement the clinical diagnosis whereasComputed tomography, magnetic resonance imaging(MRI), and ultrasonography (US) scan can be usedto confirm the diagnosis.1US scan is found to be areliable and accurate method to assess the thicknessof the masseter muscle.7 Treatment of MMH rangesfrom conservative to invasive therapy. Mild casesdo not require any treatment, or at timesreassurance or tranquilizers will help; however insevere cases botulinum toxin type A injections orsurgery can be considered. In few cases, where stressis observed, psychological follow up may be requiredin association with other treatments. 1

CASE REPORTA 55 year old female patient, reported with a

complaint of progressive swelling of right and leftlower half of the face which became more pronouncedon clenching. The swelling become increasinglyprominent over the preceding years. Patient alsocomplained of dull, aching, intermittent pain onclenching her teeth. The swelling was initiallynoticed 5 years back following menopause and hasprogressed to the present state (Fig 1). There wasno history of trauma, paraesthesia, xerostomia,trismus, dysphagia, or difficulty with masticationand speech. Patient complained of stress followingloss of a family member and was on antidepressantssince 2 months. She complained of early morningstiffness of the jaw, since three months. Onquestioning the patient admitted to bruxism. Shewas a chronic tobacco chewer and used to chewtobacco 4- 5 times /day regularly since ten years.Family history was non contributory.

Clinical examination revealed bilateral illdefined facial fullness in the region of the massetermuscle. On palpation the swelling was non tenderand no thrills or bruits were elicited. Bimanualpalpation and palpation during contraction showedthe mass to correspond to the outline of the massetermuscle. On clenching, the swelling became moreprominent and firm, and it was well appreciated onthe left masseteric region. The opening and closingof jaws were normal. There was no evidence of

midline shift or occlusal disharmony. Intraorally, afree and clear salivary flow exited from the rightand left stenson duct. Attrition was noticed inrelation to maxillary and mandibular posteriorteeth, suggestive of bruxism.

Based on the history and clinical examination,a provisional diagnosis of bilateral masseter musclehypertrophy was given. Benign parotid tumors,lipoma, vascular tumors, and temporomandibulardisorders were considered under the differentialdiagnosis. Panoramic radiograph revealed slightprominence of the right and left angle of themandible (Fig 2). Occlusal attrition in relation tomaxillary and mandibular posteriors was suggestiveof bruxism. Anteroposterior radiograph revealed thepresence of bone spur in the left angle of themandible (Fig 3). US scan showed a compensatoryhypertrophy in the area of muscle insertion due tothe increase in masseter muscle size and tension.The right masseter muscle measured 20.5 mm inrelaxed state and 22.2 mm in contracted state andthe left masseter muscle measured 20.0 mm inrelaxed state and 24.7 mm in contracted state (Fig4a, b and Fig 5a, b). The site of measurement wasin the thickest part of the masseter muscle, close tothe level of the occlusal plane, approximately in themiddle of mediolateral distance of the ramus. CTscan contiguous nonenhanced axial and coronalimages obtained from the level of hyoid bone to thelevel of temporo-mandibular joints revealed bilateralmasseter muscle hypertrophy and a small bony spurwith mild expansion of the underlying bone on theouter cortex of the left ramus of the mandible. Mildirregularity and thickening of the cortex was alsoobserved (Fig 6). The maximum thickness ofmasseter muscle was 21mm on the right side and24 mm on the left side (axial sections).

Based on the above findings, a final diagnosisof bilateral masseter muscle hypertrophy was given.The patient was advised to quit the tobacco chewinghabit, was put on muscle relaxants and was referredfor psychiatric consultation. Prosthetic crowns wereadvised to correct the occlusal attrition. She wasreferred to dermatology for cosmetic correction ofthe facial hypertrophy, but the patient refusedbecause aesthetics was not her priority.

DISCUSSION

MMH is an asymptomatic, benign enlargementof one or both masseter muscles. Some authorssuggest that the use of the term hypertrophy may

Bilateral Masseter Muscle Hypertrophy Sujatha S Reddy, et, al.

Indian J Dent Adv 2012; 4(2) 870

be misleading, because the enlargement of themuscle is caused by an increase in the number offibres and not increase in the cell size.1 Most of theMMH cases reported in the literature have occurredusually in late adolescence or early adulthood, butour patient developed MMH following menopauseat the age of 51 years. The precise etiology of MMHis not clear. Several authors claim that emotionalstress results in chronic forceful clenching of the jawsand bruxism, which cause a work hypertrophy ofthe masseter muscle.8 Our patient also complainedof stress due to some personal problem, withevidence of bruxism and severe attrition of all theupper and lower posterior teeth. Bruxism along withtobacco chewing habit in our patient might haveinduced bilateral hypertrophy of the massetermuscle. Furthermore, long standing cases usuallyexhibit hyperostosis at the bony attachment of themasseter muscle as seen in our case. Guggenheimand Cohen reported that bone spurs are caused byperiosteal irritation and new bone depositionresponding to increased forces exerted by the musclebundles.8 MMH is known to occur in isolation or withtemporalis muscle hypertrophy, but temporalishypertrophy without hypertrophy of massetermuscle is very rare. Change in facial appearance isthe most frequent complaint of patients with MMH.Though hypertrophy is probably the most commoncause of isolated enlargement of the massetermuscle, consideration should be given to thepossibility of inflammation, neoplasia, or, rarely,malignant infiltration. Occasionally, masseterichypertrophy can be misdiagnosed as parotitis ormalignant neoplasm.2

Diagnosis of masseter hypertrophy cannot solelybe based on clinical findings alone, CT, MRI andUS scan can be used to confirm the diagnosis. CTand MRI are useful in determining the extent andlocation of bucco-masseteric masses. CT scanning isindispensable in case of MMH with bone flaring, dueto its high quality imaging of bony structures anddirect bone imaging, but is not possible with MRIbecause cortical bone produces no significant signal.The salient distinguishing feature is the associatedbony changes i.e. hyperostosis at the site of muscleattachment, in benign masseteric hypertrophy.8 CTscan in our patient demonstrated a small bony spurarising from outer cortex of the left ramus of themandible with mild expansion of the underlyingbone. US scan evaluation revealed increased MMthickness on both sides in relaxed and contractedstate, compared to that of unaffected individuals.7

Microscopic examination of the excised muscle tissueusually shows normal muscle fibres without changesin length, thickness, or nuclear structure.Zachariades et al reported two cases in whichphleboliths were associated with masseteric musclehypertrophy.1

MMH is a benign condition and therapy isusually not required. Non –surgical modalities oftreatment include reassurance, tranquilizers,spasmolytics or muscle relaxants, psychiatric careand injection of very small doses of botulinum toxintype A. Botulinum toxin A is a powerful neurotoxinwhich is produced by the anaerobic organismClostridium botulinum and when injected into themuscle causes interference with theneurotransmitter mechanism producing selectiveparalysis and subsequent atrophy of the muscle.6

The action of this therapy may be temporary, newneuromuscular synapses may be resynthesized overa period of few months and antibodies may developbecause of the repeated injections.1 It is also anexpensive therapy and should be considered as anoption only for those who have complicated ordisabling bruxism and are refractory to othermedical and dental therapy.9 Dental restorationsand occlusal adjustment to correct prematurecontacts and malocclusions are important. Para-functional habits must be prevented.8 A more radicalapproach to treating MMH consists of partial muscleresection, usually in the lower portion using eitherthe intraoral or extraoral approach. Some authorshave recommended concomitant reduction orresection of the prominent mandibular angle. Thedisadvantage of surgical reduction includes the risksof general anaesthesia, postoperative haemorrhage,oedema, hematoma, infection, scarring, and facialnerve damage.1 Following treatment, follow up isrequired because this condition can be recurrent.

CONCLUSION

MMH is a relatively rare condition of unknowncause and it should be considered under thedifferential diagnosis of head and neck masses,located in the cheek. Early diagnosis of MMH isimportant so that the patient and parents can beinformed about the likely development of facialasymmetry and further progression prevented.

ACKNOWLEDGEMENT

We would like to thank our Principal andProfessor Dr. H. N. Shama Rao and our Head of theDepartment Dr. Yashoda Devi B.K. for their supportand guidance.

Bilateral Masseter Muscle Hypertrophy Sujatha S Reddy, et, al.

Indian J Dent Adv 2012; 4(2) 871

Fig 1: Photographs showing progressive massetermuscle hypertrophy over the years

Fig 2: Panoramic radiograph showing sharp right and left mandibularangle with attrition of upper and lower posterior teeth.

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masseter muscle hypertrophy: A case report. QuintessenceInt 2002; 33: 776-779.

2. Fyfe EC, Kabala J, Guest PG. Magnetic resonance imagingin the diagnosis of asymmetrical bilateral masseterichypertrophy. Dentomaxillofac Radiol 1999; 28: 52-54.

3. Addante RR. Masseter Muscle Hypertrophy: Report of caseand Literature review. J Oral Maxillofac Surg 1994; 52:1199-1202.

4. Skoura C, Mourouzis C, Saranteas T, Chatzigianni E,Tesseromatis C. Masseteric hypertrophy associated withadministration of anabolic steroids and unilateralmastication: A case report. Oral surg Oral Med Oral PathOral Radiol Endod 2001; 92 : 515-518.

5. Rispoli DZ, Camargo PM, Pires Jr JL, Fonseca VR, MandelliKK, Pereira MAC. Benign masseter muscle hypertrophy.Rev Bras Otorrinolaringol 2008; 74(5): 790-793.

6. Bas B, Ozan B, Muglali M, Celebi N. Treatment ofmasseteric hypertrophy with botulinum toxn: A report oftwo cases. J Oral Maxillofac Pathol 2010; 15: 649-652.

7. Ariji E, Ariji Y, Yoshiura K, Kimura S, Horinouchi Y, KandaS, et al Ultrasonographic evaluation of the inflammatorychanges in the masseter muscle. Oral Surg, Oral Med, OralPath Oral Radiol Endod 1994; 78: 797-801.

8. Sannomiya EK, Goncalves M, Cavalcanti MP. MasseterMuscle Hypertrophy-Case Report. Braz Dent J 2006; 17:347 -350.

9. Tan KE, Jankovie J .Treating severe bruxism withbotulinum toxin. J Am Dent Assoc 2000; 131: 211-216.

Fig 3: Antero posterior view showing developmentof bone spur in the left angle of the mandible.

Fig 5a: US scan showing left masseter musclemeasuring 20 mm in relaxed state

Fig 4a: US scan showing right masseter musclemeasuring 20.5 mm in relaxed state

Fig 4b: US scan showing right masseter musclemeasuring 22.2 mm in contracted state

Fig 5b: US scan showing left masseter musclemeasuring 24.7 mm in contracted state

Fig 6: CT scan showing masseter hypertrophy and smallbony spur in the left angle of the mandible (coronal view).

Bilateral Masseter Muscle Hypertrophy Sujatha S Reddy, et, al.