Urol Radiol 13:190-193 (1992)

Urologic Radiology © Springer-VedagNewYorkInc. 1992

Retrovesical Leiomyoma: CT and Contrast-Enhanced MR Imaging Findings S. Thurnher, t B. Marincek, Land D. Hauri z Departments of ~Medical Radiology and 2Urology, University Hospital, Zfirich, Switzerland

The computed tomographic (CT) and magnetic resonance (MR) appearance o f a retrovesical leiomyoma in a male patient is presented. Although leiomyomas are common lesions, the location within the retrovesical pouch is very unusual.

Abstract.

Key words: Leiomyoma -- Pelvis, abnormalities -- Computed tomography -- Magnetic resonance

imaging.

Leiomyoma is a mesothelial tumor composed of whorls of smooth muscle cells [1]. It occurs in all age groups and shows no sex predominance. The tumor may arise in any structure of the body, most commonly in the uterus, gastrointestinal tract, retroperitoneum, and skin [1]. Within the genitourinary system, the kidney capsule is the most common location [2]. However, the origin in the retrovesical pouch is extremely rare with few cases reported in the world literature [2--4]. We present a case of an asymptomatic retrovesical mass consistent with leiomyoma on magnetic resonance (MR) imaging. Case Report A 70-year-old man presented to another hospital with a palpable mass on routine pelvic examination. He was free of symptoms. Clinical examination revealed a nontender mass, which on bimanual palpation under anesthesia was continuous and superior to the enlarged prostate gland. Uroflow was normal. Rectal mu-

Address offprint requests to: Dr. S. Thurnher, Universit~itsklinik Cfir Radiodiagnostik, Allgemeines Krankenhaus, Alser Strasse 4, A-1090 Wien, Austria

cosa was movable and did not show any sign of infiltration. Urinalysis and urine cultures were normal. An intravenous pyelogram showed no displacement of the distal ureters and no signs of urinary obstruction. Abdominal sonography demonstrated a large lobulated mass in the right pelvic area. Computed tomography (CT) of the pelvis revealed a noncalcified mass with a hypodense central zone, posterior to the bladder and superior to the prostate gland. Impression of the posterior bladder wall and displacement of the right seminale vesicle was noted (Fig. 1). Panendoscopy demonstrated an elongated and compressed urethra, elevated floor of the bladder, and impression of the right posterior bladder wall. The patient was referred to our hospital for further evaluation and treatment. M R imaging was performed with a 1.5 T Gyroscan S 15 imaging system (Philips, Eindhoven). On precontrast Tl-weighted spin-echo (SE) images (repetition time, T R = 500 msec; echo time, TE = 20 msec), the retrovesical mass exhibited homogeneous low-signal intensity similar to piriformis muscle. Thickened mucosa was noted in the region of the right orifice. On T2-weighted (TR 2000 msec; TE 80 msec) images, the tumor was ofinhomogeneous low- to medium-signal intensity with a central hypointense irregular area (Fig. 2A). After intravenous administration of 0.1 mmol/kg Gd-DOTA (Guerbet SA, Aulnay-sous-bois, France), moderate enhancement of the mass was noted on Tl-weighted MR images (Fig. 2B and C). The centrally located zone remained hypointense. Transabdominal resection of the mass revealed a 7 x 7 x 5 cm retrovesicaI encapsulated tumor. The mass appeared to originate from the right seminale vesicle or base of the prostate gland, because both organs were attached to the mass. However, surgical detachment was possible. The posterior wall of the bladder was not fixed to the tumor. The mucosa of the bladder trigonum showed a hemorrhagic and vesicular appearance. Finally, a ureterocystoneostomy was performed because of encasement of the fight distal ureter. Macroscopically, the cut surface was whitish in color with wavy bundles and multiple nodules. Histopathology revealed a benign leiomyoma. The tumor was composed of interlacing bundles of spindle-shaped cells with eosinophilic cytoplasma and regular, oval nuclei. No mitoses were present. Postoperatively, the patient did well. Recent follow-up 9 months after the initial presentation revealed the patient to be free of symptoms.

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Fig. 1. Axial CT scan shows large mass (T) in the retrovesical pouch, impressing the posterior wall of the urinary bladder (B). On a more cephalad image, hypodense intratumoral areas were present (not illustrated).

Discussion

The retrovesical pouch is an uncommon site of primary tumors in male patients. More frequently, direct extension of prostatic and rectum carcinoma or metastases does occur in this region. Leiomyomas may originate from any anatomic location of smooth muscle in the genitourinary system. In the retrovesical pouch the determination of exact origin of leiomyomas is difficult to establish in most cases [3]. Bladder leiomyomas, which are the most common benign mesothelial bladder tumors, develop as submucosal, intramural, or external growths [2, 5]. Extramural leiomyomas may become very large and are attached to the bladder by a small pedicle. In our patient we believe that the origin of the tumor was in the capsule of the right seminale vesicle or base of the prostate gland due to its close attachment to these structures. However, the origin from smooth-muscle fibers of pelvic soft tissue or posterior bladder wall could not be totally excluded. The CT appearance ofleiomyomas (e.g. of uterine origin) is that of a well-delineated soft tissue mass. Calcifications within the tumor may be suggestive ofleiomyoma. However, calcifications found in most of the masses occur in the retrovesical pouch. In our patient no calcification was present on CT. The M R appearance of leiomyomas is well established in the uterus [6]. Owing to its histologic features, leiomyomas are imaged with low-signal intensity on T1- and T2-weighted M R images. As hyaline, myxomatous, or fatty degeneration occurs, they demonstrate an inhomogeneous appearance on

T2-weighted M R images. The tumors exhibit mixed low- and high-signal intensity with hyperintense degenerative intratumoral zones. The pattern in this case was similar to uterine leiomyomas. The mass presented with homogeneous low-signal intensity on T 1-weighted M R images. On T2-weighted M R images, the central portion of the tumor was of highsignal intensity, which proved to be degenerative changes on histologic analysis. The intravenous administration of paramagnetic contrast agents facilitates the evaluation of complex pelvic tumors over unenhanced M R imaging [7]. In our study improved demonstration of intratumoral architecture was achieved following administration of Gd-DOTA. The enhancement pattern of the retrovesical mass was moderate and inhomogeneous, with a central nonenhancing portion. The round and well-demarcated mass suggested a benign dignity. Even though the correct histological diagnosis was not possible by M R imaging, additional information regarding tumor origin could be achieved. The concave configuration of the posterior bladder wall and the close attachment of the mass to the right seminale vesicle and prostate gland suggested an extravesical origin of the mass. Leiomyomas may be difficult to differentiate from other tumors arising in the retrovesical pouch. The differential diagnoses include primary tumors of the seminal vesicle (e.g., congenital cyst, carcinoma, fibrosarcoma) [8], bladder (e.g., fibroma, myxoma, hemangioma, carcinoma, sarcoma) [2, 4], prostate gland (e.g., carcinoma), rectum (e.g., carcinoma), or Miillerian duct remnant tumors [9]. The

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Fig. 2. A T2-weighted axial MR image (TR 2000 msec; TE 80 msec) shows medium signal intensity mass (7) with central hyperintense zone, representing degenerative changes. B Postcontrast axial Tl-weighted MR image (TR 500 msec; TE 20 msec) shows moderately enhancing tumor (7) with attachment to the right seminale vesicle (S). Urinary bladder (B); thickened mucosa of bladder wall around right orifice (arrow). C Postcontrast sagittal Tl-weighted MR image (TR 500 msec; TE 20 msec) shows the mass (7) superior to the prostate gland (P), impressing posterior wall of the bladder (B). Degenerative nonenhancing intratumoral zones (arrows). M R characteristics o f soft tissue m a s s e s in the pelvis are well established [6, 7]. T o o u r knowledge, o n l y a few papers a d d r e s s e d the a p p e a r a n c e o f retrovesical m a s s e s o n M R i m a g i n g [8, 9]. Cystic lesions, h e m a n g i o m a s , or c a r c i n o m a s usually exhibit highsignal intensity o n T 2 - w e i g h t e d M R images. H o w ever, f i b r o m a s o r s a r c o m a s m a y be d e m o n s t r a t e d with signal intensity characteristics similar to t h o s e o f o u r p a r t i c u l a r patient. Histopathological differentiation between l e i o m y o m a a n d l e i o m y o s a r c o m a m i g h t be a difficult task [1]. I n o u r case the a b s e n c e o f m i t o s e s a n d s y m p t o m - f r e e p o s t o p e r a t i v e interval indicates the b e n i g n h i s t o l o g y o f the mass. W e suggest t h a t l e i o m y o m a s s h o u l d be i n c l u d e d in the differential diagnosis, w h e n a solid retrovesical m a s s is e n c o u n t e r e d in the retrovesical p o u c h

in m a l e patients. M R i m a g i n g m a y be useful in d e m o n s t r a t i n g the origin o f the mass.

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S. Thurnher et al.: Retrovesical Leiomyoma of MR, histopathologic findings, and symptoms. Radiology 158:385-391, 1986 7. Thurnher S, Hodler J, Baer S, Marincek B, von Schulthess GK: Gd-DOTA-enhanced MR imaging of adnexal tumors. J Comput Assist Tomogr 14:439-449, 1990

193 8. King BF, Hattery RR, Lieber MM, Williamson B, Hartman GW, Berquist TH: Seminal vesical imaging. Radiographics 9: 653-676, 1989 9. Thurnher S, Hricak H, Tanagho EA: Miillerian duct cyst: Diagnosis with MR imaging. Radiology 168:25-28, 1988