Teaching Case

A 53-year-old woman presented with painless swelling of the right gluteal region. The lesion had come to her gynecologist's attention during a routine pelvic examination. The vaginal mucosa on the right side of the posterior fornix was bulging inward. There were no signs of retraction or ulceration.

MR images delineated a well-defined, oval-shaped mass in the right ischiorectal fossa, which measured 12.5 x 5.0 x 3.5 cm. It was closely attached to the posterolateral aspect of the right pelvic diaphragm. On the T1-weighted images the mass presented with low signal intensity, similar to that of skeletal muscle. After intravenous injection of gadopentetate dimeglumine the mass revealed an intense and homogeneous enhancement on the contrast-enhanced T1 weighted images. On T2-weighted images the mass presented with high signal intensity and curvilinear darker signal intensity areas within the tumour. The associated mass effect caused a circumscribed impression of the pelvic floor leading to a partial obliteration of the fat between the pelvic floor and the tumour.
US of the perineal region revealed a hypoechogenic mass in the right ischiorectal fossa. CEUS revealed a vascular pedicle originating from the right pelvic diaphragm with an early intense centripetal enhancement.

With our patient included, 138 cases of an angiomyofibroblastoma (AMFB) have been reported so far and the patients presented with an average of 45 years at initial examination [1]. After surgical excision local reoccurrence was not noted, but it has to be mentioned that the mean follow-up timespan never exceeded 12 months [1]. A female-to-male ratio of 10:1 was reported by Wolf et al. [1]. Regarding the female gender, the preferred location of growth of an AMFB is the vulva [1].

AMFBs and other pelvic soft tissue tumours are rare entities that can easily be confused with other, more common vaginal masses, such as Bartholin’s cyst, rectocele, or urethral diverticulum [2]. However, based on variable imaging modalities these benign lesions can easily be set apart from solid masses by demonstrating an intralesional vascularization. Considering the differential diagnosis of masses in the perineal area by Menias et al. [2] and having in mind the imaging criteria of the above mentioned mass in the ischiorectal fossa, the aggressive angiomyxoma (AMX) seems to have a very similar appearance.

The AMX was first described by Steeper and Rosai in the year 1983 and arises mostly in the pelvic and perineal region. It commonly affects women of reproductive age. These tumours typically present as large masses with unusual expansile growth pattern. Especially the pattern of translevator extension is reported to be suspicious for this aggressive tumour that is prone to local recurrence after resection [3]. On MR-images these entities present with low signal on T1-sequences and high signal intensity on T2-sequences with some kind of darker linear laminated structures in between. Cystic appearance as well as intense enhancement on the postcontrast images was described [4, 5]. Surabhi et al. found the above mentioned imaging features on MRI suggestive for the diagnosis of an aggressive angiomyxoma.

Our patient’s tumour was excised in toto and regular follow-up imaging was unremarkable. As described, an angiomyofibroblastoma may present with very similar signal intensities and enhancement patterns on MRI. The aggressive growth pattern (translevator extension) of the aggressive angiomyxoma in contrary to the more circumscribed mass-like growth pattern in angiomyofibroblastoma may be the features to differentiate these two entities, so radiographers should especially focus on these characteristics. Even in our case, where the angiomyofibroblastoma was closely attached to the pelvic diaphragm, helpful tools to rule out translevator extension were B-mode ultrasound with and without colour Doppler as well as contrast-enhanced ultrasound.