Clinical History
A 69-year-old man presented to his assistant doctor complaining about lower quadrants abdominal pain. He didn´t have gastrointestinal, nor urinary symptoms. He had a history of hypertension and benign prostatic hyperplasia, and no relevant family history. Physical examination revealed a hard palpable mass in the right lower quadrant.
Imaging Findings
Contrast-enhanced computed tomography (CT) scan revealed a predominantly solid well-defined mass in the right upper pelvis (Figures 1-5), measuring about 9.2 x 7.2 x 7.0 cm. The mass had lobulated margins without signs of rupture, and heterogeneous contrast enhancement, with hyperenhanced and hypoenhanced / nonenhanced areas (Fig. 1). The mass had contact with the distal ileal loops, including the terminal ileum (Fig. 3), without invasion or relevant pressure effect, and displaced neighbouring organs, namely the bladder (Fig. 4), the right ureter, and the sigmoid colon (Fig. 5). No metastases, lymphadenopathies, ascites or peritoneal implants were detected.
Complete surgical excision was performed and histology revealed a mesenchymal neoplasm consisting of spindle cells immersed in a collagenic stroma. The cells assumed a multifocal dense fascicular pattern alternating with hypocellular areas with a haemangiopericytoid vascular pattern. There were foci with 5 mitoses /10 HPF, and the cells were positive for CD34, CD99, Bcl2 and CAM5.2.
Discussion
Solitary fibrous tumours (SFTs) are an uncommon group of mesenchymal neoplasms with fibroblastic or myofibroblastic origin. Although SFTs frequently occur in the pleura, they can originate in virtually any site of the body [1]. Extrapleural SFTs commonly occur in the retroperitoneum, abdominal cavity, deep soft tissue of extremities and head and neck [2]. Pelvic SFTs are rare entities that usually arise from the peritoneum or prostate gland [1].
Extrapleural SFTs usually occur in middle-age adults and manifest as asymptomatic, slow growing, large tumours. Patients with abdominal or pelvic tumours may present with pain, a palpable mass, or symptoms due to pressure effect like urinary retention or obstruction, constipation or bowel obstruction [1, 2]. Some tumours (<5%) may manifest with severe hypoglycaemia related to excessive production of insulin-like growth factor by the tumour (Doege-Potter syndrome) [3].
CT is the modality of choice for detection of abdominal and pelvic SFTs. SFTs commonly appear as well-circumscribed, hypervascular masses that may displace or exert pressure effects on neighbouring organs. Central hypoenhancing or nonenhancing areas may be present, representing necrosis or cystic changes. Besides being useful in the primary diagnosis, CT helps to depict local extent, and to detect locoregional and distant metastases. At magnetic resonance imaging, SFTs usually have intermediate signal intensity on T1-weighted images and heterogeneous low signal intensity with flow voids on T2-weighted images [1, 2]. After administration of gadolinium contrast material, SFTs usually are hypervascular tumours with intense enhancement. However, the enhancement pattern on dynamic contrast-enhanced images can vary widely depending on cellularity, vascularity, and the density of the collagenous stroma of the tumour. Hypervascular areas enhance intensely, the hypercellular areas show moderate enhancement, and areas of necrosis and cystic degeneration do not enhance [1].
Imaging studies are not usually sufficient to differentiate SFTs from other abdominal and pelvic tumours, and hence histology and immunohistochemistry remain the best diagnostic markers [2, 4]. SFTs are composed of juxtaposed hyper- and hypocellular spindle cell proliferation, dense collagenous stroma, and numerous thin-walled blood vessels with a staghorn configuration (haemangiopericytoid vascular pattern) [1]. SFTs usually show strong and diffuse staining for CD34, Bcl2 and vimentin [5].
Surgical excision is the treatment of choice for SFTs, with an overall 5-year survival around 90% with complete surgical excision [1, 3]. About 10-15% of SFTs demonstrate aggressive behaviour in the form of recurrence or malignancy [1]. Criteria of malignancy are high cellularity, nuclear atypia, high mitotic activity (>4/10 high powered field) and necrosis [5].
Differential Diagnosis List
Extrapleural solitary fibrous tumour
Gastrointestinal Stromal Tumour (GIST)
Desmoid tumour
Leiomyosarcoma
Malignant mesothelioma
Final Diagnosis
Extrapleural solitary fibrous tumour
