GASTROINTESTINAL STROMAL TUMOUR (GISTs)

Commonly occur in the stomach and duodenum. Previously named leiomyoma and leiomyosarcoma, the term GIST is now used. The tumours are universally associated with a mutation in the tyrosine kinase c-kit oncogene. These tumours  are sensitive to the tyrosine kinase antagonist imatinib, and an 80%  objective response rate can be observed.   The biological behavior of these tumours is unpredictable but size and mitotic index are the best predictors of metastasis. Peritoneal and liver metastases are most common; spread  to lymph nodes is extremely rare.

The incidence of small stromal tumours of the stomach are probably quite common but remains unnotced. Clinically obvious tumours are considerably less common than gastric cancer.

The only way that many tumours ulcerate to bleed or that they are noticed incidentally at endoscopy. Larger tumours present with nonspecific gastric symptoms and, in many instances, it may initially be thought that they are gastric cancer.

Treatment: Surgery is curable for small tumour. Larger tumour may need gastrectomy or duodenectomy but lymph adenectomy is not required.  

Larger tumour may be better treated for 3-6 months with imatinib before operation as this will usually reduce their size and vascularity.

The prognosis  of advanced metastatic GIST has been dramatically improved with imatinib chemotherapy.

GASTRIC LYMPHOMA

Gastric lymphoma is an interesting disease and some aspects of the management are controversial. It is important to distinguish primary gastric lymphoma from involvement of the stomach in a generalized lymphomatous process. The latter situation is more common than the former. The incidence of the disease is increasing. Primary gastric lymphoma accounts for about 5% of all gastric neoplasms.

Clinical features

Gastric lymphoma is most prevalent in the sixth decade of life. The presentation is no different from gastric cancer, the common symptoms are Pain, Weight loss and Bleeding. Acute presentation of gastric lymphoma such as haematemesis, perforation or obstruction  are not common. Primary gastric lymphoma remains in the stomach for a prolonged period before involving the lymph nodes. At an early stage, the disease takes the form of a diffuse mucosal thickening, which may ulcerate.

Diagnosis

Diagnosis is made from endoscopic biopsy and seldom on the basis of the endoscopic features alone , which are not specific.

Following diagnosis, adequate staging is necessary, primarily to establish whether the lesion is a primary gastric lymphoma or part of a more generalised process. CT scans of the chest and abdomen and bone marrow aspirate  are required, as well  as a full blood count.

TREATMENT

Although the treatment of the primary gastric lymphoma is somewhat controversial, it seems most appropriate to use surgery alone for the localized disease process. No benefit has been shown from adjuvant chemotherapy; although some oncologist contends that primary gastric lymphoma can be treated by chemotherapy alone. Chemotherapy alone is appropriate for patients with systemic disease.

Some of the more controversial aspects of gastric lymphoma concern the role of  H. pylori. It has been shown that early gastric lymphomas may regress and disappear when the Helicobacter infection is treated.

Gastric operations for morbid obesity:

Morbid obesity is defined as being 100% over the ideal weight for height or having a body mass index

[(wt in kg)/(ht in metre)2] of greater than 45. It is an increasing and major health problem in the west specially in USA. A number of surgical treatments have been devised for morbid obesity, but none is free of problems. Selection of patients for operation should ideally be made by a team that includes a nutritionist/endocrinologist and a psychiatrist, as well as surgeon, because it is important that major metabolic problems and severe psychiatric disorders are elucidated before operation. Morbidly obese patient as defined above have an excessive morbidity and mortality.

The patient will often already have morbidity, associated with severe obesity, such as hypertension, diabetes or osteoarthritis. Preoperative counseling should include perioperative mortality. This is very much an elective procedure and the patient is at risk of postoperative respiratory problems and pulmonary thromboembolism. Thromboembolic prophylaxis are essential as are antibiotics.

Increasingly, surgery is performed laparoscopically. The two most common preformed procedures are the Lap Band procedure & Gastric Bypass.

In the Lap Band procedure an inflatable cuff is placed laparoscopically just below the oesophagogastric junction. The inflation of the band determines the level of restriction.

However, very small differences in volume may result in complete dysphagia on the one hand and no significant weight loss on the other. Perioperative mortality is less than 1%. Band slippage may cause problems and the long term results seem inferior to conventional surgery.

The operation that has the best long term result is gastric bypass. The operation can be performed laparoscopically and, although technically difficult, it is becoming a standard procedure for the severely obese. Using a combination of circular and linear staplers, a gastric pouch is created. The pouch has no connection to the rest of the stomach but is drained by a 70cm Roux loop. The operative mortality is in the region of 2%.

After both procedures the patient must be managed in a high dependency care unit until the possibility of apnoea and others complication diminished. Epidural anesthesia is useful as it decreases opioid requirements. The may be introduced to fluids and some food on the first postoperative day. Dietary advice is important; the patient must understand that liquidized food or high calorie supplements are to be avoided. The patient should lose between on third and one half of their body weight over 2 years. Vomiting is common and vitamin supplementation is advised. 

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