Urol Radiol 5:253-259 (1983) Urologic Radiology

© Springer-Verlag 1983

Pitfalls Related to the Urinary Bladder in Pelvic Sonography: A Review

C. Whitley Vick, Gregory N. Viscomi, Eric Mannes, and Kenneth J.W. Taylor Department of Radiology, Yale University School of Medicine, New Haven, Connecticut, USA

Abstract. A number of pitfalls related to the uri- nary bladder may be encountered during ultra- sound examination of the pelvis. Examples of par- ticularly difficult or frequently encountered situa- tions are illustrated in this report. In our experi- ence, difficulties most commonly arise from incor- rect identification of the urinary bladder, with an abnormal cystic pelvic mass simulating the normal urinary bladder, or vice versa. In addition, confus- ing appearances may be caused by urine refluxed into the vagina, technical artifacts, bladder diverti- cula, or mobile pelvic masses displaced by the blad- der. Definitive bladder identification is useful to avoid errors in situations likely to be associated with bladder related pitfalls.

Key words: Pelvic ultrasonography - Bladder ul- trasound studies - Pitfalls, ultrasound studies.

A distended urinary bladder is a prerequisite as an acoustic window for a successful pelvic ultra- sound examination. However, the filled bladder is occasionally responsible for adding confusion to the interpretation of the pelvic scan. The bladder, a bladder diverticulum, or urine refluxed into the vagina may be mistaken for a pathologic pelvic mass. A fluid-filled viscus such as the bladder fre- quently gives rise to reverberation artifacts which may simulate a pathologic fluid collection or mass. In addition, extravesical cystic masses or fluid col- lections may mimic the bladder and mislead the ultrasonographer.

Address reprint requests to: C. Whitley Vick, M.D., Department of Diagnostic Radiology, Virginia Commonwealth University/ Medical College of Virginia, Box 615 MCV Station, Richmond, VA 23298

This report reviews and illustrates pitfalls in pelvic sonography related to the urinary bladder. The cases shown exemplify particularly difficult or frequently encountered problems one may expect to see in an active ultrasound practice.

Materials and Methods

Twelve hundred patients were referred for pelvic ultrasonogra- phy between July, 1980 and June, 1982. Commercially available static and dynamic gray-scale equipment was used. All patients undergoing pelvic ultrasound were requested to report after drinking 680 ml water, although patient compliance was vari- able. The cases in this report illustrate some of the difficulties which arose in these patients.

Case Reports

Cystic Mass Simulating Urinary Bladder - Case 1

An asymptomatic 15-year-old girl was referred for a possible pelvic mass. Pelvic ultrasound was interpreted as normal, al- though the right ovary was not recognized (Fig. 1). At surgery the following day, a 15-cm right ovarian mucinous cystade- noma was removed. In retrospect, the urinary bladder probably can be seen compressed beneath the cystadenoma (Fig. 1 B).

Case 2

Pelvic ultrasound in a 26-year-old female renal transplant recip- ient showed 2 fluid collections, the larger of which simulated the bladder because of its shape and anterior location (Fig. 2). However, a postvoid scan definitively identified the smaller col- lection as the bladder, and needle aspiration showed that the larger collection represented a sterile lymphocele.

Bladder Mimick ing a Pelvic Mass - Case 3

A 64-year-old diabetic woman was referred because of weight loss and a large pelvic mass on physical examination. There was no history of voiding difficulty. The patient complained of intense urinary urgency during pelvic sonography which showed a large cystic pelvic mass. She voided an unknown quantity of urine in the bathroom and returned much relieved

254 C.W. Vick et al. : Pitfalls in Bladder Sonography

Fig. 1. Ovarian cystadenoma simulating the bladder. A Transverse pelvic scan demonstrates the uterus (U) and left ovary (containing a small cyst) posterior to a cystic mass (C) thought to represent the bladder. B Longitudinal scan. The cystic mass (C) proved at surgery to represent a right ovarian cystadenoma. In retrospect, the urinary bladder (arrow) is probably seen compressed beneath the mass

Fig. 2. Lymphocele simulating the bladder. A Longitudinal pelvic scan shows two fluid collections, the larger of which (L) simulates the bladder. U, uterus. B A postvoid scan definitively identifies the smaller collection as the bladder. The larger collection (L) proved to be a lymphocele

with no urinary urgency. No change in the size of the cystic mass was detected on postvoid scans (Fig. 3). Therefore, the diagnosis of a large cystic pelvic mass was made, and it was assumed that the bladder was compressed beneath the mass. However, an intravenous urogram the next day showed that this pelvic "mass" actually represented a massively distended urinary bladder. In retrospect, the postvoid scan might have been correctly interpreted if the amount of urine voided had been documented.

Urine Refluxed into the Vagina - Case 4

An 11-year-old girl underwent pelvic ultrasound for a question- able pelvic mass palpated by the patient's pediatrician. The patient denied enuresis, and pelvic examination done by a gyne- cologist was normal. A fluid collection adjacent to the postero- inferior bladder margin was identified on initial scans (Fig. 4A). The collection grew in size and the bladder became smaller after the patient voided once (Fig. 4B). After voiding twice,

C.W. Vick et al.: Pitfalls in Bladder Sonography 255

Fig. 3. Bladder mimicking a pathologic mass. This longitudinal postvoid scan of the pelvis shows a large fluid collection anteri- or to the uterus (u). Because the patient reported that voiding had completely relieved urinary urgency, a pathologic mass was suspected. However, a urogram subsequently showed that this "collection" actually represented an atonic bladder distended with urine

both the bladder and the adjacent fluid collection emptied. Be- cause of these findings, the fluid collection was thought to rep- resent a bladder diverticulum. However, a voiding cystoure- throgram demonstrated that the collection actually was due to urine refluxed into a capacious, but normal, vagina (Fig. 4C and D).

Discussion

Errors in pelvic sonography related to the urinary bladder may potentially arise from incorrect identi- fication of the urinary bladder, bladder diverticula, urine refluxed into the vagina, mobile pelvic masses, or technical artifacts.

In our experience, the majority of potential er- rors related to the urinary bladder stem from incor- rect identification of the bladder. If an abnormal cystic pelvic mass is mistaken for the normal uri- nary bladder, a false-negative sonogram may re- sult, as in case 1 [1-5]. The incidence of this type of error is not precisely known, but in 1 series of 100 cystic pelvic masses greater than 7 cm in diameter, only 1 pathologic mass was misinter- preted as the bladder [1]. The normally compliant urinary bladder is easily compressed and displaced laterally or caudally by adjacent masses [1]. Such a mass may then assume the normal anterior, mid- line position of the bladder and, if cystic, may look

identical to the urinary bladder (Fig. 1). Definitive identification of the urinary bladder is necessary to avoid a false-negative or equivocal study (Fig. 2). The most common cystic pelvic masses we have encountered which simulate the bladder are ovarian cystadenomas and lymphoceles. Other cystic masses to consider include a simple ovarian or paraovarian cyst, ovarian cystadenocarcinoma, urinoma, hematoma, abscess, fluid-filled bowel, endometrioma, and (rarely) mesenteric or serosal cyst, necrotic ovarian neoplasm, or pancreatic pseudocyst [2-6]. A rectus sheath hematoma orig- inating or extending inferior to the linea semicircu- laris (located approximately midway between um- bilicus and pubis and marking the caudal extent of the posterior rectus sheath) may extend into the fascial cleft between bladder and symphysis pu- bis (the space of Retzius), causing displacement of the bladder [7]. This type of hematoma may simulate the appearance of the bladder (Fig. 5).

Ascites may also mimic the bladder or a cystic pelvic mass on static images (Fig. 6) [4, 8]. This type of pitfall usually can be avoided with dynamic scanning which readily demonstrates the character- istic appearance of ascites as it insinuates itself around and between organs and bowel loops [1, 4,6,8].

Mistaking a distended urinary bladder for an abnormal cystic pelvic mass may result in a false- positive sonogram (Fig. 3) [9-11]. Because the bladder is the most commonly encountered cystic pelvic structure, a distended bladder should be considered in the differential diagnosis of any cys- tic pelvic mass [10, 12]. This pitfall may be avoided by definitive bladder identification.

In the absence of any contrast medium, identifi- cation of the urinary bladder by ultrasound may be presumptive or definitive. The bladder is pre- sumptively identified by its characteristic position, shape, and size [4, 10]. Presumptive bladder identi- fication suffices for the majority of pelvic sono- grams in situations not usually associated with bladder related pitfalls (Table 1). Definitive blad- der identification by ultrasound requires documen- tation of a change in bladder volume or identifica- tion of a catheter within the bladder lumen. In general, we consider definitive identification im- portant in any clinical situation likely to be asso- ciated with a bladder related pitfall (Table 1). Uri- nary urgency, or lack thereof, and the patient's previous voiding history should not dissuade one from definitively identifying the bladder in the ap- propriate clinical setting (Case 3) [5, 12]. Tech- niques to change bladder volume for definitive identification are well known and include (in order

256 C.W. Vick et al. : Pitfalls in Bladder Sonography

Fig. 4. Vaginal reflux of urine. A Longitudinal prevoid scan of the pelvis shows a fluid collection (c) behind the bladder (B). B After the patient voided once, the collection (c) becomes larger and the bladder (B) smaller. After the patient voided twice, both the collection and the bladder emptied. The collection was suspected to represent a bladder diverticulum. C and D Sequential films from a voiding cystourethrogram show reflux of contrast from the bladder into a capacious vagina (arrowheads) during voiding

of increasing effort or invasiveness): voluntary voiding, physiological filling, and catheterization either to empty or fill the bladder. It is important to document the amount of urine voided in order to interpret postvoid scans correctly. In addition, prior to catheterization one should search for a caudally displaced and compressed urinary bladder by scanning low in the pelvis (Fig. 1 B) [1]. A mir-

ror-image artifact may be seen beneath the bladder on longitudinal scans of the pelvis, and this artifact should not be mistaken for a compressed urinary bladder beneath an abnormal cystic mass (Fig. 7).

A well-known technical artifact related to the bladder is caused by reverberation produced by total reflection of sound at the interface between the posterior bladder wall and adjacent gas in the

C.W. Vick et al.: Pitfalls in Bladder Sonography 257

Table 1. Situations potentially associated with bladder-related pitfalls

Physical exam/ultrasound discrepancy Mass on physical exam not on ultrasound Mass on ultrasound not on physical exam

Two or more fluid collections in pelvis

Following surgery predisposing to pelvic fluid collections Renal transplantation recipients Pelvic lymphadenectomy

"Bladder" containing debris or septae

Patients prone to urinary retention Recent surgery Elderly Diabetic Medication

Ascites

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Fig. 5. This 65-year-old man developed a new pelvic mass 5 days after being put on intravenous heparin therapy. A transverse scan of the pelvis demonstrates 2 fluid collections, the larger of which (H) simulates the appearance of a distended urinary bladder. However, the larger collection was later shown to represent a rectus sheath hematoma which developed below the linea semicircularis. Definitive identification of the urinary bladder (b) was made on a postvoid scan

Fig. 6. Ascites simulating the bladder. A Transverse static scan of the pelvis shows what was initially thought to be the bladder with a possible fluid collection posteriorly. B Longitudinal scan shows that the findings in A are actually due to ascites (A) with interposed bowel loops (B). The collapsed urinary bladder was identified on more caudad scans

rectosigmoid colon [13, 14]. Reverberation of sound occurs between the bladder-wall-bowel-gas interface and the transducer-skin interface, and the reverberated echoes, which are detected later in time than the initially returning echoes, are inter- preted by the instrument as having arisen deeper in the body [13, 14]. The reverberation pseudomass (or bladder duplication artifact) which results may

appear cystic, or it may contain echoes (Fig. 8). Such artifacts are usually easy to recognize because of their periodic quality and progressively weaker signals, but occasionally a reverberation pseudo- mass may be difficult to differentiate from a patho- logic pelvic mass [13, 14]. In such cases, useful maneuvers include scanning the apparent mass at different angles and planes, changing the volume

258 C.W. Vick et al. : Pitfalls in Bladder Sonography

Fig. 7. A mirror-image artifact (A) may be seen beneath the bladder base on longitudinal pelvic scans. This artifact should not be mistaken for the urinary bladder (B) compressed beneath a pelvic mass

Fig. 8. A 45-year-old man with a questionable pelvic mass seen on urography. A A longitudinal pelvic scan shows the bladder (B) and striking reverberation pseudomasses (P) posteriorly. B The pseudomasses are no longer seen on a longitudinal scan made with the bladder (B) less full

of the bladder, or using a water bath. One of these will usually cause a pseudomass to change in con- figuration or to disappear entirely (Fig. 8 B). In ad- dition, physical examination will often clarify any appearances which are still equivocal.

If the communicat ion between a bladder diver- ticulum and bladder is not demonstrated, the di- verticulum may appear to represent a cystic mass adjacent to the bladder [14]. Static scanning at closely spaced intervals or careful dynamic scan-

ning usually identifies the communicat ion between diverticulum and bladder, allowing one to make a correct diagnosis. Postvoid scans may show ei- ther complete emptying or a variable degree of uri- nary retention within the diverticulum [15].

Urine that refluxes into the vagina may mimic a pathologic fluid collection (Fig. 4) [16]. The ap- pearance may mistakenly suggest the diagnosis of a cul-de-sac mass, hemoculpos, or a Gartner 's cyst. In addition, as in case 4, the appearance of a blad-

C.W. Vick et al.: Pitfalls in Bladder Sonography 259

der diverticulum may be simulated. Vaginal reflux of urine is familiar to pediatric radiologists who observe young girls voiding in the supine position during voiding cystourethrography [16]. Since this maneuver is not usually performed during pelvic sonography, refluxed urine in the vagina is not often seen on ultrasound. However, one may antic- ipate seeing refluxed vaginal urine if inadvertent partial emptying of the bladder occurs in a supine patient during pelvic sonography [16].

A mobile pelvic mass may not be detected by pelvic ultrasound if it is displaced into the abdo- men by the distended urinary bladder [17]. Scan- ning the lower abdomen or allowing the mass to descend into the pelvis after partially emptying the bladder will usually correctly identify such masses [171.

Acknowledgements. The authors thank Pauline E. Friedman for manuscript preparation, Linda Alcebo, R.T., R.D.M.S., and James Sivo, B.S., R.D.M.S., for technical assistance.

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