SMALL BOWEL MALIGNANCY

**SMALL BOWEL MALIGNANCY **

1. Small bowel malignancy refers to primary malignant tumors arising in the duodenum, jejunum or ileum.

2. Classification of small intestinal malignancies:
   a. Adenocarcinoma – most common in duodenum and proximal jejunum.
   b. Carcinoid (neuroendocrine) tumor – frequent in distal ileum.
   c. Gastrointestinal stromal tumor (GIST) – arises from interstitial cells of Cajal.
   d. Lymphoma – often associated with immunodeficiency or celiac disease.
   e. Sarcoma – rare, includes leiomyosarcoma and others.

3. Epidemiology:
   a. Overall incidence 1–2 per 100 000 population per year (≈1‑2 % of GI cancers).
   b. Slight male predominance for adenocarcinoma; carcinoid shows slight female predominance.

4. Risk factors:
   a. Age >50 years.
   b. Hereditary syndromes – Lynch (HNPCC), Peutz‑Jeghers, familial adenomatous polyposis.
   c. Chronic inflammatory conditions – Crohn’s disease, celiac disease.
   d. Prior radiation exposure.
   e. Lifestyle – high‑fat diet, smoking, alcohol (mainly for adenocarcinoma).

5. Pathophysiology:
   a. Genetic mutations (APC, KRAS, TP53) lead to dysplasia → carcinoma in adenocarcinoma.
   b. Neuroendocrine cells undergo hyperplasia → carcinoid.
   c. KIT or PDGFRA mutations drive GIST development.
   d. Lymphoid proliferation in response to chronic antigenic stimulation may transform to lymphoma.

6. Routes of spread:
   a. Direct local invasion into mesentery, pancreas or adjacent bowel.
   b. Lymphatic dissemination to mesenteric, para‑aortic and retroperitoneal nodes.
   c. Hematogenous spread – liver, lung, bone.
   d. Peritoneal seeding in advanced disease.

7. Clinical features (often nonspecific):
   a. Intermittent abdominal pain, usually post‑prandial.
   b. Unexplained weight loss and anorexia.
   c. Signs of obstruction – nausea, vomiting, abdominal distension.
   d. Occult or overt gastrointestinal bleeding → melena or anemia.
   e. Carcinoid syndrome (flushing, diarrhea, wheezing) if metastatic.

8. Diagnostic methods:
   a. Barium small‑bowel follow‑through – shows filling defects or strictures.
   b. Endoscopic techniques – push enteroscopy, double‑balloon enteroscopy for direct visualization and biopsy.
   c. Cross‑sectional imaging – contrast‑enhanced CT abdomen/pelvis (detects mass, nodal disease, metastasis).
   d. MRI enterography – superior soft‑tissue contrast, useful in young patients.
   e. 18F‑FDG PET/CT – assesses metabolic activity and distant spread, especially for lymphoma and GIST.
   f. Histopathology with immunohistochemistry – confirms tumor type (e.g., CD117 for GIST, chromogranin for carcinoid).

9. Complications:
   a. Acute or chronic intestinal obstruction.
   b. Massive gastrointestinal bleeding leading to anemia or hemorrhagic shock.
   c. Perforation with peritonitis.
   d. Malabsorption and severe nutritional deficiency.
   e. Metastatic disease causing organ dysfunction (hepatic failure, respiratory compromise).

10. Prognostic factors:
    a. Tumor histology and grade (high‑grade adenocarcinoma or lymphoma worse prognosis).
    b. Stage at presentation – localized disease has best outcome.
    c. Tumor size >5 cm and depth of invasion correlate with poorer survival.
    d. Presence of regional nodal involvement or distant metastasis.
    e. Resection margin status – negative margins improve survival.

11. Treatment overview:
    a. Surgical resection is the mainstay for localized tumors.
    b. Adjuvant chemotherapy is considered for high‑grade adenocarcinoma and lymphoma.
    c. Radiotherapy has limited role, mainly for palliation of symptomatic metastases.
    d. Targeted therapy – imatinib or sunitinib for KIT/PDGFRA‑mutated GIST; somatostatin analogues for symptomatic carcinoid.
    e. Palliative measures – endoscopic stenting, blood transfusion, pain control for unresectable disease.

12. Surgical treatment steps (flow format):
    Pre‑operative preparation → bowel cleansing and prophylactic antibiotics → exploratory laparotomy (or minimally invasive laparoscopy) to locate tumor and assess spread → segmental resection of involved bowel with adequate margins → mesenteric lymph node dissection → restoration of continuity by hand‑sewn or stapled end‑to‑end anastomosis → intra‑operative assessment for hemostasis and leak → postoperative monitoring for anastomotic integrity, nutrition and early mobilization.