Carcinoid Tumor & Small Bowel Neoplasms

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In the context of small bowel malignancies, carcinoid tumors are the most prevalent primary cancer. These neoplasms originate from neuroendocrine cells and often manifest in the ileum, but may be found in the stomach, colon, appendix, and even lungs. In fact, bronchial carcinoid tumors are the most common primary lung cancer in children. On histology, carcinoid tumors appear as islands of small, round, purple cells embedded in pink connective tissue. Electron microscopy reveals cytoplasmic granules containing secretory products and hormones.

In the GI tract, carcinoid tumors can cause intestinal obstruction or appendicitis. Carcinoid syndrome is associated with the release of vasoactive substances like serotonin and histamine. Notably, the symptoms of carcinoid syndrome—episodic flushing, vascular telangiectasias, secretory diarrhea, bronchospasm, and right-sided valvular heart disease—arise when the tumor metastasizes beyond the GI tract or liver, thereby bypassing first-pass metabolism. Diagnosis is confirmed through the presence of urine 5-HIAA. Treatment typically involves somatostatin analogues like octreotide.

Small bowel adenocarcinomas most commonly occur in the duodenum and present with glandular structures on histology. Risk factors for this malignancy include familial adenomatous polyposis (FAP), Lynch syndrome, and Crohn’s disease, with the latter often affecting the ileum. Peutz-Jeghers syndrome, an autosomal dominant disorder that causes non-neoplastic hamartomatous polyps throughout the GI tract, can also lead to small bowel adenocarcinoma. It presents with characteristic mucocutaneous hyperpigmentation in the mouth, lips, palms, and genitals.

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What are carcinoid tumors and where can they occur?

Carcinoid tumors are the most common primary small bowel malignancy. They derive from neuroendocrine cells and can occur in several locations like the stomach, colon, lungs, ileum (most common site), and appendix. They can also occur in the lungs, resulting in bronchial carcinoid tumors— the most common primary lung cancer in children.

How does carcinoid syndrome occur and what are its symptoms?

Carcinoid syndrome is caused by the secretion of vasoactive substances like histamine and serotonin from carcinoid tumors. This happens when the tumor metastasizes to the liver or beyond the GI tract, bypassing first-pass metabolism by the liver. Symptoms include episodic flushing of the face, neck, chest due to excessive histamine secretion, vascular telangiectasias on the nose and cheeks from vasodilation, secretory diarrhea from excessive serotonin, episodic bronchospasm and wheezing, and valvular disease in the right heart due to excessive serotonin.

How is carcinoid syndrome diagnosed and treated?

Carcinoid syndrome is diagnosed using urine 5-HIAA (5-hydroxyindoleacetic acid), a breakdown product of serotonin. The syndrome is treated using somatostatin analogues like octreotide which inhibit the release of serotonin.

What is small bowel adenocarcinoma and what are its risk factors?

Small Bowel Adenocarcinoma is a malignant tumor formed from glandular structures in the small bowel. The duodenum is the most common site for these carcinomas. Risk factors include Familial Adenomatous Polyposis (FAP), Lynch Syndrome, Peutz-Jeghers Syndrome, which is autosomal dominant that causes hamartomatous polyps throughout the GI system and mucocutaneous hyperpigmentation, and Crohn’s disease.

How do carcinoid tumors present on histopathologically?

On gross pathology, carcinoid tumors appear yellow. Histologically, these tumors contain islands of small round purple cells within pink connective tissue. On electron microscopy, the carcinoid tumor cells display cytoplasmic granules, which contain secretory products and hormones. The tumors may cause intestinal obstruction in the case of small bowel carcinoid tumors or appendicitis when blockage occurs in the appendiceal lumen.