Gastrointestinal stromal tumors (GISTs) account for < 3% of gastrointestinal neoplasms and are the most common mesenchymal tumors of the gastrointestinal tract¹. They occur in patients > 50 years with male predominance, are usually benign in 70- 80% and occur in the stomach and small intestine in up to 90% of the cases. Yet, GISTs may develop in the mesentery, omentum, retroperitoneum, gallbladder, bladder wall or uterus².

We report the case of a patient with a mesenteric GIST. A 56-year-old male patient sought medical care for abdominal pain in the right iliac fossa that appeared after exercising 10 days before. The patient was a current smoker, obese, had a history of hypertension (HTN) and diabetes (DBT) and was treated with anticoagulants due to a previous stroke and arrhythmia. On physical examination, the vital signs were within normal parameters. The abdomen was nontender and depressible without costovertebral angle tenderness. A non-tender, hard-elastic and immobile mass was palpated in the right hypochondrium and right iliac fossa.

The laboratory tests showed INR of 3.5; creatinine level 0.65 mg/dL; BUN 0.25 g/L; LDH 460 U/L; hemoglobin level 14.4 g/dL; hematocrit 42.9%; white cell count 6.26 K/uL (67/21/9/2/1); urinalysis with absence of leukocytes; CA 19-9, CEA, alpha-fetoprotein (AFP) and beta subunit were negative. Work-up began with a posteroanterior erect radiography of the abdomen and chest. Due to the absence of air-fluid levels, gas under the domes of the diaphragm or thickening and edema of the bowel wall, a more sensitive test was performed.

A computed tomography (CT) scan showed an expansive mass within the peritoneum in the center of the abdomen, in close contact with the small bowel loops. The lateral diameter of the mass was 14 cm, the anteroposterior diameter was 15 cm, and the cephalocaudal diameter was 17 cm. The entire colon seemed to be intact. The mass presented peripheral enhancement and a hypodense, apparently necrotic, central area.

There were multiple rounded hypodense lesions with rosette-like enhancement involving the left and right hepatic lobes with diameters between 10 and 20 cm, suggestive of liver metastases. The initial diagnoses were tumor versus spontaneous hematoma of the mesentery due to incorrect management of anticoagulation (Fig. 1).

Figure 1 A: Contrast-enhanced computed tomography scan of the abdomen. An abdominal mass is seen in the axial section (arrow) B: Contrast-enhanced computed tomography scan of the abdomen. An abdominal mass is seen in the sagittal section (arrow) 

As the patient continued with pain and hemoglobin levels were decreasing despite transfusions, surgical management was decided. An exploratory laparotomy was performed. A tumor was found in the mesentery extending towards its root and attached to the small intestine. The extension of the tumor was greater than expected and there were lesions suggestive of peritoneal implants. The procedure continued with bowel resection, en bloc resection of the mesenteric tumor, Brooke ielostomy and omentectomy (Fig. 2 A, B). The pathological examination of the surgical specimen reported:

▪ Peritoneal implants: two solid specimens; the smaller one was more friable.

▪ Intra-abdominal tumor: mesenchymal neoplasm made up of spindle-shaped cells and epithelial cells diffusely arranged within a hyaline stroma with necrotic areas.

▪ The omentum was free of tumor involvement. Immunohistochemistry of the specimen showed positive staining for smooth muscle actin (+) and CD 117 (+) (Fig. 2 C).

Figure 2 A: Anterior surface of the surgical specimen. B: Posterior surface of the surgical specimen. C: Histological section Giemsa-stained 40x (see description in the text) 

The patient was admitted to the hospital ward with a vital and functioning ileostomy, tolerating oral feeding, and was discharged on day 5 with scheduled controls in the nutrition, psychology, oncology and general surgery clinics. Visits were scheduled twice a month during the first month, monthly for 3 months and every 3 months until the first year was completed. The patient continued attending the oncology clinic under treatment with imatinib for up to 1 year, and was then lost to follow-up. The natural history of GISTs is still unknown. Because symptoms and signs are unspecific, they are usually found incidentally as 60% are asymptomatic³. Extra GISTs represent 5% of all GISTs and are histologically and immunophenotypically similar; however, they have a worse prognosis⁴, as in our case, not only because of the type of location in the mesentery, but also because they are large tumors measuring > 5 cm, with atypical presentation and imaging tests findings.

Diagnosis depends on morphological and immunohistochemical findings. Morphological features include predominance of spindle-shaped cells (70%), epithelioid cells (20%), or a mixed type (10%). In addition, 95% of GISTs are positive for KIT (CD117) or discovered on GIST-1 (DOG1), while 70% are positive for CD34. When immunohistochemistry shows negative staining for KIT, as in approximately 5% of GISTs, positive staining for DOG1 and CD34 staining, make the diagnosis. KIT and PDGFRA mutations are other important molecular markers.

The radical treatment is surgical resection. Imatinib is the treatment of choice for inoperable or disseminated tumors⁵. Phase II/III studies are currently ongoing to determine its usefulness in adjuvant and neoadjuvant therapy². As treatment interruption is associated with high risk of recurrence, lifelong therapy is required².