Adenocarcinoma of the Small Bowel
Adenocarcinoma of the Small Bowel
A 16-year-old female patient with repeated vomiting. First X-ray of the abdomen shows multiple dilated small bowel loops, represent distal small bowel obstruction. CT of the abdomen done for further evaluation.
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Partial small bowel obstruction, adhesive band. Tiny rather vascular tumor and a follow up will be required for this patient. In view of the fact that this patient is young, MRI could be used as a follow-up examination. Patient has no family history of similar disease or risk factors.
Patient was operated and 48 cm of small intestine removed and end-to-end anastomosis done.
Poorly differentiated adenocacinoma.
Primary adenocarcinoma of the jejunum is an uncommon tumor, and the peak incidence is in 50- and 60-year-old patients. Nevertheless, we cannot eliminate this type of lesion from consideration in young patients. Few cases were reported previously.
Malignant neoplasms of the small bowel are among the rarest types of cancer, accounting for only 2 percent of all GI cancers. Research into the natural history and prognosis of patients with small-bowel cancer has been limited by the small number of cases and the heterogeneity of tumor types, including adenocarcinomas, carcinoids, sarcomas, and lymphomas. Each of these tumor subtypes has its own distinct clinical behavior and, therefore, dictates a different treatment approach. Unfortunately, malignant lesions are often discovered when they have metastasized to distant sites or at surgery when indicated for other diagnosis or intestinal obstruction.
Approximately 64 percent of all small-bowel tumors are malignant, and approximately 40 percent of these tumors are adenocarcinomas. Epidemiologically, small-bowel adenocarcinomas have a striking resemblance to large-bowel adenocarcinomas. For example, although small-bowel adenocarcinomas are only one fiftieth as common as large-bowel adenocarcinomas, they share a similar geographic distribution, with predominance in Western countries. In addition, they tend to co-occur in the same individuals, with an increased risk of small-bowel adenocarcinoma in survivors of colorectal cancer and vice versa.
Furthermore, similar to adenocarcinomas in the colon, those in the small bowel arise from premalignant adenomas. This occurs both sporadically and in the context of familial adenomatous polyposis. Through a stepwise accumulation of genetic mutations, these adenomas become dysplastic and progress to carcinomas in situ and then to invasive adenocarcinomas. They then metastasize via the lymphatics or portal circulation to the liver, lung, bone, brain, and other distant sites.
Despite these similarities with colon cancer, small-bowel adenocarcinomas tend to cluster away from the colon, toward the gastric end of the small intestine. Approximately 50 percent arise in the duodenum, 30 percent in the jejunum, and 20 percent in the ileum. The duodenum is the first portion of the small bowel to be exposed to ingested chemicals and pancreaticobiliary secretions. This fact, combined with the higher prevalence of cancer in the duodenum, may indicate that the substances (ie, ingested chemicals, pancreaticobiliary secretions) may have carcinogenic properties. Animal studies have demonstrated that diverting bile decreases the prevalence of experimentally induced small-bowel cancers, which suggests that bile may be carcinogenic.
The five-year overall survival rate for patients with adenocarcinoma has been estimated to be 30 percent to 35 percent. The five-year survival rate for patients with small-bowel sarcomas is approximately 25 percent.
Men have higher rates of all types of small bowel cancer than women do, with a male-to-female ratio of 1.4:1. The prevalence of small-bowel cancer tends to increase with age, with a mean age at diagnosis of approximately 60 years. Adenocarcinomas, more than the other histologic subtypes, tend to be diagnosed in somewhat older patients
Small-bowel cancer is typically asymptomatic in its early stages, but more than 90 percent of patients eventually develop symptoms as the disease progresses. This unfortunately reflects advanced disease. Because of the nonspecific nature of symptoms, a significant delay between the onset of symptoms and diagnosis often occurs, averaging 6 to 8 months. Nausea, vomiting, and intestinal obstruction are common presenting symptoms. Half of these patients undergo emergency surgery for intestinal obstruction. Abdominal pain and weight loss complicate the clinical presentation. Bleeding is less common.
The few published series on small bowel neoplasms that are available cannot be used as generalizations for presentation of the individual histologic subtypes. However, it does appear that adenocarcinomas are more frequently associated with pain and obstruction when compared to sarcomas and carcinoids. Sarcomas (GIST) present more commonly with acute GI bleeding.
Patients with small-bowel malignancies may present with fairly unremarkable physical examination findings. A tender and distended abdomen may be found due to obstruction. Peritoneal signs indicate perforation. Jaundice from biliary obstruction or liver metastases may occur rarely. Guaiac-positive stool or acute GI bleeding, suggests intestinal bleeding, although this occurs more frequently in persons with benign small-bowel tumors.
Genetic risk factors
• Familial adenomatous polyposis
• Hereditary nonpolyposis colorectal cancer
Environmental risk factors
• Diet: A 1977 study by Lowenfels and Sonni found animal fat intake to be correlated with small-bowel cancer. Another study, in 1993 by Chow et al, reported that consumption of red meat and salt-cured or smoked foods raised the risk of small-bowel cancer 2-3 times.
• Tobacco and alcohol: Studies from 1994 by Chen et al found an association between smoking and small-bowel adenocarcinoma and between alcohol consumption and small-bowel adenocarcinoma, but this has not been confirmed in other studies.
Predisposing medical conditions
• Crohn disease:
• Peutz-Jeghers syndrome: Hemminki has reported an approximately 18-fold increase in the incidence compared to that in the general population.
Sushila Ladumor, MD, FRCR, Consultant Radiologist with Multi-modality Imaging experience, working in Medical Imaging Department, King Abdulaziz Medical City, Riyadh, Saudi Arabia.