Bilateral giant extragastrointestinal stromal tumour of the retroperitoneum

Gastrointestinal stromal tumours (GISTs) are mesenchymal neoplasms that can appear in any segment of the gastrointestinal (GI) tract and account for 0.1–3% of all GI tumours. They can be benign and malignant, and there are three histological types: spindle, epithelial, and mixed-cell [1]. Almost all GISTs express immunopositivity for CD117, a C-Kit proto-oncogene protein, which shows an increase in the function of C-Kit gene, which encodes growth factor receptor with tyrosine kinase activity [2]. Extragastrointestinal stromal tumours (EGISTs) are extremely rare neoplasms with histopathological and immunohistochemical features similar to GIST. However, they are found outside the GI tract, in the omentum, retroperitoneum, or mesentery with no evidence of a primary GI neoplasm, and without connection to the intestinal wall [3]. Less than 60 cases of EGIST localised in retroperitoneum are currently documented in English literature [4].
We present a case of giant bilateral retroperitoneal EGIST in a 58-year-old male patient.
A 58-year-old obese male presented with a six-month history of abdominal discomfort. Ultrasound depicted hydronephrosis grade II in the right kidney and large tumour mass (around 20 cm) in the projection of the left kidney. Magnetic resonance imaging (MRI) depicted two tumour masses: one adjacent to the left kidney measuring 20 × 18 × 25 cm, which filled Gerota’s fascia and suppressed nearby structures in the opposite direction; and another, paracaval mass on the right side measuring 50 × 39 × 35 mm, compressing the right ureter causing grade II hydronephrosis, which required percutaneous nephrostomy. Renal vasography showed that the tumour mass in the left retroperitoneum did not originate from the kidney, and extirpation of this giant tumour was performed.
Grossly, the tumour measured 22 × 20 × 16 cm and weighed 2 kg (Figure 1). It was lobulated with adipose tissue on the surface. The cut surface revealed a fish flesh appearance with focusses of degeneration and haemorrhage. Tissue was fixed in 4% neutral formaldehyde, embedded in paraffin, cut into 4-µm sections, and stained with haematoxylin-eosin. An immunohistochemical analysis was performed and included: CD117, vimentin, actin, Anti-MYO D1, CD34, MelanA, S-100, CD68, CD57, CD31, LCA, and CKAE1/AE3.
Histologically, the tumour was mostly hypercellular, composed of short and fusiform spindle cells, with light cytoplasm and elongated nuclei (Figure 2). They were...


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