Abstract
Gastro-inestinal stromal tumours (GISTs) comprise 1–2% of all gastrointestinal (GI) tumours. The mesentery, retroperitoneum and omentum are common sites of extra-gastrointestinal stromal tumours (E-GISTs). Isolated involvement of the mesentery by tuberculosis (TB) without any evidence of pulmonary disease is quite unusual. Here we report a case of an E-GIST arising from the small bowel mesentery in a 60-year old female where an incidental concurrent mesenteric tuberculosis was diagnosed following surgical resection.
Introduction
GISTs are the commonest mesenchymal tumours in the gastro-intestinal tract, usually occuring after 50 years of age.1,2 Their usual sites are stomach (56%) and small intestine (32%). GISTs have been found to be associated with certain non-neoplastic conditions, some of which include myasthenia gravis and pulmonary tuberculosis.3,4
Case history
A 60 year old female presented with complaints of fever and abdominal swelling for six months. The swelling was insidious in onset, painless and progressively increasing in size. Abdominal ultrasonographic examination demonstrated a large heterogenous abdomino-pelvic mass in the right abdomen. On CT scan this measured 14 × 13 × 12 cms in the right lumbar and iliac region showing peripheral enhancing soft tissue component with foci of calcification and a central area of hypodensity with multiple mottled air densities, suggestive of GIST [Figure 1(a)]. Full blood count and basic biochemical parameters were within normal limits. Carcinoembryonic antigen (CEA) and CA125 were found to be normal. Ultrasound-guided fine needle aspiration cytology demonstrated a spindle cell tumour, closest to GIST [Figure 1(b)].
(a) CECT abdomen showing heterogenous mass lesion in right lumbar region showing peripherally enhancing component with foci of calcification and central areas of hypodensity. (b) FNAC from the mesenteric mass showing fascicles of spindled tumour cells exhibiting mild nuclear pleomorphism; (c) Photomicrograph showing proliferation of spindle shaped cells in sheets and fascicles. (H&E,x200)(inset showing cut section of the tumour with areas of hemorrhage and areas of necrosis); d) Immunohistocemical stain for CD117 showing diffuse cytoplasmic positivity in tumour cells (x400).
As our patient subsequently complained of severe acute abdominal pain, an emergency laparotomy to limit probable tumour rupture was performed. The mesenteric mass was excised with resection of small bowel leaving end ileostomy amd distal mucous fistula. The ileocaecal junction, caecum and ascending colon were adherent to the mass. The remaining gut and solid organs were normal.
On gross pathological examination, the mass had a 15 cm maximal diameter, and its cut section was largely grey white, soft to firm, solid with focal grey brown, necrotic areas. [Figure 1c]. Histopathologic examination showed a cellular mesenteric tumour composed of whorls and interlacing fascicles of spindle cells having pale, eosinophilic fibrillar cytoplasm along with elongated, vesicular nuclei [Figure 1(c)]. Scattered mitotic figures were noted (2–3/50hpf). The overlying intestine was unremarkable. On immune-histochemical staining with CD117, the tumour cells showed diffuse cytoplasmic positivity [Figure 1(d)]. The surrounding mesentery showed epithelioid cell granulomata along with large areas of caseating necrosis and Langhans giant cells [Figure 2(a)]. In view of extensive caseation necrosis, Ziehl Neelsen staining was performed which showed the presence of acid fast bacilli within the necrosis [Figure 2(b)]. Peritoneal tuberculosis was therefore diagnosed. Screening by chest radiography demonstrated no pulmonary foci. Four-drug antitubercular treatment was continued for nine months with satisfactory resolution of the disease.
(a) Photomicrograph showing epithelioid cell granulomas, Langhans giant cells and foci of caseation necrosis in the surrounding mesentery adjoining tumour (H&E,x200); (b) Ziehl Neelsen stain showing presence of acid fast bacillus. (ZN,x1000).
Discussion
The immuno-histochemical and ultrastructural characteristics of GISTS are different from other mesenchymal tumours. 5 They arise from pluripotent mesenchymal stem cells, the interstitial cells of Cajal, which form a neural network within the submucosal and muscular layers of the GIT. 6
Certain theories have been postulated regarding origin of E-GISTs based on their imunophenotype and clinicopathological behaviour. Some authors consider these tumours as GISTs being separated from the gastrointestinal tract, while few others believe them to be as primary growths from the mesentery or omentum. The latter is explained on the basis of presence of ICC-like cells in the omentum. 7
The co-existence of non-syndromic GIST with other diseases has not been extensively explored. Plausible hypotheses suggest that one condition predisposes to the other. An immune-compromised state due to cancer and its therapy is known to activate latent TB. 8 Tuberculosis, on the other hand, induces a chronic inflammatory state in the host, leading to cytokine production which can further stimulate development of neoplasia.
