Teaching Case

A 66-year-old man was referred to our hospital for a six-month pelvic discomfort with nocturia and urinary urgency. A soft mass was palpable on rectal examination located superiorly and to the right of the prostate. There was no reference to rectal bleeding or bowel disorders.

Computed Tomography (CT) displayed a retrovesical solid mass with heterogeneous enhancement, measuring 10 cm in longest longitudinal diameter. The mass was independent of the bladder and rectum, cranial to the prostate. It was unclear the relationship with the seminal vesicles (Fig. 1). No calcifications were seen.

Magnetic Resonance Imaging (MRI) of the pelvis confirmed a well-circumscribed mass superior to the prostate without infiltration. The mass probably aroused from the right seminal vesicle and completely replaced it.  This tumour deviated the left seminal vesicle laterally. The lesion was heterogeneous hyperintense on T2-weighted images (WI). It was predominantly iso-intense to the muscle on T1-WI with hyperintense scattered focus on both T1-WI and fat-suppressed T1-WI, suggesting underlying haemorrhage.

The patient underwent complete resection, and the diagnosis was compatible with a perivascular epithelioid cell tumour (PEComa) of the right vesicle seminal at histopathological examination.

PEComas represent a broad spectrum of rare mesenchymal tumours, including angiomyolipoma, lymphangioleiomyomatosis, and clear cell epithelioid tumours [1].

These tumours are composed of different types of cells focally associated with blood vessel walls and usually express melanocytic and smooth-muscle markers. Pecomas arise from perivascular nests of distinctive epithelioid or spindle cells, exhibiting the deletion of chromosome 16p, associated with tuberous sclerosis 2 gene [1,2].

The majority behave as benign tumours, but some are potentially malignant [1,2].

Folpe et al. described as worrisome features for malignancy the presence of two or more criteria: (1) dimension (>5 cm), (2) infiltrative growth partner, (3) high nuclear grade and cellularity, (4) mitotic rate >1/50 high power fields, (5) necrosis and (6) vascular invasion [3].

Most of the PEComas are sporadically, and syndromic cases occur associated to tuberous sclerosis [2].

The prevalence peak is in young to middle-aged adults with a mean age of 45, with a female predominance [1].

PEComas distribution is ubiquitous and may arise in any anatomical site, being more common in the kidney, especially in cases of tuberous sclerosis, and in the uterus [4]. Prostate and vesicle seminal PEComas are extremally rare and a just few cases were reported [5].

Symptoms are non-specific and related to the localization; patients could also be asymptomatic [4].

PEComas manifest as a solitary soft-tissue mass with intense contrast enhancement on contrast-enhanced CT and MRI. On MRI, they also show a variable T2 signal intensity [1, 4].

Double-echo gradient-echo MRI could demonstrate the presence of microscopic fat tissue. Fat-suppressed T1-WI sequences help to determine the presence of macroscopic fat tissue and haemorrhage [4].   Intense diffusion restriction is often associated with malignancy [1].

CT and MRI were not specific enough to establish the diagnosis, and biopsy or surgical excision was necessary.

Complete resection is usually curative and careful surveillance is recommended. Recurrence has been associated with large tumours with infiltrative margins [1].

PEComas should be considered in the differential diagnosis of large well-circumscribed genito-urinary tumours.