GUT STROMAL TUMOUR- Presenting as Pain in the Abdomen



	Tumours of small bowel are relatively uncommon representing only 3% to 6% of all gastrointestinal neoplasms. Most series report a slight preponderance of malignant neoplasms over benign neoplasms. Leiomyomas are the most common benign neoplasm of the small intestine.1 Pathologists have begun to shift from the terms leiomyoma and leiomyosarcoma to the term stromal cell tumour.2 Gut stromal tumours (GST) are intramural bowel tumours of low malignant potential. They were formerly known as leiomyomas and leiomyosarcomas because of their light microscopic appearance which mimicked smooth muscle, however in pathology literature they have recently been termed as GST because the site of origin is not known, i.e. smooth muscle, nerve, mesenchyme or just stromal. These tumours arise from the bowel wall usually from between the muscularis

propria and muscularis mucosae and may expand towards the bowel lumen, serosa or in both directions (dumb bell shaped).3

The commonest site for these gastrointestinal stromal tumours is stomach (39%) followed by small intestine (32%), rectum (10%), large intestine (5%), others (mesentery, omental, oesophagus, diaphragm), intestine unspecified (5%).4 In the small intestine it is commonest in the jejunum followed by ileum, duodenum and Meckel’s diverticulum. Male to female ratio is almost equal, the peak incidence being 50 to 59 years.2 Symptoms of GSTs are as follows - 41% are detected incidentally (autopsy or surgery), 59% are symptomatic, the symptoms being as follows - gastrointestinal bleeding (acute and chronic), abdominal pain, bowel obstruction, weight loss, mass, perforation.3 Laboratory studies rarely reveal specific abnormalities in patients with small bowel neoplasms.5

Commonly used procedures for diagnosis have been endoscopy and upper gastrointestinal series, although these procedures have produced inconsistent results in the past. Endoscopy was correct in 13% to 33% of the times and barium contrast studies were correct 25% to 29%.2

An intramural leiomyoma is shown on barium studies as round smooth intraluminal filling defect. A serosal neoplasm is recognized as a mass attached to the intestine indenting the lumen and causing displacement of adjacent barium filled loops of intestine. Dumbbell leiomyoma demonstrate the combined features of intraluminal and serosal neoplasms.6 The main features of leiomyosarcoma on barium examination is large cavity filled with barium and it may be difficult to identify the connection between the small intestine and cavity.6

Leiomyomas appear on CT as round sharply demarcated, homogeneous masses that are chiefly extrinsic to the lumen. They are of uniform soft tissue attenuation but a small proportion contain amorphous calcification.1

On CT, a leiomyosarcoma usually appears as a large, heterogeneous, predominantly solid mass withmultiple cystic spaces (corresponding with areas of necrosis) which exhibits intense enhancement of its solid components.7

Leiomyosarcomas have similar CT features, but may show metastases to liver or spread to mesentery and peritoneum.1

Computed tomography is highly successful and when used detected 89.5% of leiomyomas and 98% of leiomyosarcomas. Both tumour necrosis and ulceration can be identified with this technique. As both benign and malignant smooth muscle tumours undergo necrosis, CT cannot differentiate between the two on this basis, but it can accurately measure the size of neoplasm. Metastases, an important indicator of malignancy, are recognized by CT and therefore help stage tumour progression.2

Selective angiography is useful for delineating subserosal tumours and those that are actively bleeding.2

Ultrasonography has also been used to diagnose these neoplasms and can locate intraluminal, intramural and extraluminal growth patterns (as well as those tumours with dumbbell shape). It also detects metastases.2

Intraluminal gut masses may have a variable appearance on sonography but are frequently hidden by gas or luminal content. In contrast gut pathology creating an exophytic mass are more readily visualized.8 Smooth muscle tumours typically procedure round mass lesions of varying size and echogenecity and often with central cystic areas. Smooth muscle tumours of gut origin should be considered in the differential diagnosis of incidentally noted, indeterminate abdominal masses in asymptomatic patients.8

Histologically, the distinction between benign and malignant tumours is difficult to make and classification of malignancy is unreliable. However two of the strongest pathologic predictors of malignant behaviour are size (generally > 5 cms) and mitotic count (generally > 5 mitoses per high power field). Even small GST with a bland, benign appearance may behave in a malignant fashion by extensive local invasion, local recurrence or metastasis.

Thus all GSTs should be considered a low grade malignancy with a small risk of recurrence and metastasis.3 Pre-operative percutaneous biopsy carries the theoretical risk of peritoneal seeding or tumour rupture.4

Patients with a very large GST (> 5 cms) should have life long follow up including periodic CT scan, due to risk of recurrence and metastasis.3
Metastatic disease is most common in liver and peritoneum. Metastasis to local lymph nodes do not occur, thus there does not appear to be a need for local lymph node dissection. As GSTs are usually radioresistant and insensitive to chemotherapeutic agents the only curative therapy is surgical excision.3

If one assumes that small GST will become larger and then symptomatic, then the frequent, often severe complications experienced by the symptomatic patient provide strong evidence to support excision of small, incidentally found tumours as well as the larger GST. Local excision with negative histological margins is recommended because of the low malignant potential of GST. These principles should be followed whether the lesion is termed a GST or leiomyoma/leiomyosarcoma.3