Radiology Resident Case of the Week
Etiology/Pathophysiology:
The carcinoid cells arise from enterochromaffin or enterochromaffin like cells in the GI tract, ovaries or lungs. 90% arise from the GI tract and the most common sites in descending order of frequency are: the appendix, terminal ileum, and rectum, with the remainder in the colon, stomach, duodenum and Meckel's diverticulum.
The enterochromaffin cells of carcinoids belong to a larger family of amine precursor uptake decarboxylators (APUD) which secrete a variety of substances including: serotonins, 5-hydroxytryptophan, histamine, catecholamines, kinins, prostaglandins, substance P and motilin, that are responsible for the carcinoid syndrome.
The carcinoid syndrome is classically described as flushing, diarrhea, and abdominal cramps, but borborygmi, cyanosis, telangiectasis, pellagra like skin lesions, wheezing, dypsnea or palpitations may also occur.
In general, the carcinoid syndrome is only associated with metastasis to the liver, but patients with ovarian teratomas and bronchial carcinoids, (whose secretory products enter into the systemic circulation), may present with the carcinoid syndrome without liver metastasis. Carcinoid tumors that are confined to the small bowel or mesentery do not produce the carcinoid syndrome, apparently because the tumor byproducts are metabolized by the liver.
Although carcinoids must be considered malignant, 25% of the cases do not metastasize.
After metastasis to the liver, carcinoids can spread to the lungs, bone, skin and almost any organ.
Pathology:
The appendix is the most common site of carcinoid tumors, and accounts for 30-40% of cases. The small bowel is the second most common site and majority of cases occur in the distal ileum.
Ileal carcinoids are often multiple, frequently metastasize and produce the carcinoid syndrome in 40%. In half of these cases, the carcinoid is associated with other malignancies. Ileal carcinoids tend to grow through the bowel wall and invade the mesentery where they produce a desmoplastic reaction leading to fibrosis and small bowel obstruction.
The obstructions are due in part to shortening of the mesentery from sclerosis and impairment of the enteric blood supply, which may result in further cicatrization, kinking and narrowing.
Miscellaneous:
Treatment consists of wide surgical excision including the adjacent mesentery. For lesions in the distal ileum, a right hemicolectomy is needed to adequately remove the lymphatic drainage.
Since small bowel carcinoids are often multicentric, the remainder of the intestine should be examined at the time of surgery.
The overall 5 year survival is 50-60% dropping to 20-35% with liver metastasis, but in some instances, patients have lived as long as 23 years after onset of symptoms.
Imaging:
The appearance of carcinoids can vary from a benign appearing submucosal mass to a large bulky ulcerating lesion with deformity of the bowel. A smoothly rounded polyp seen in the terminal ileum should always be considered a probable carcinoid, because such tumors may be assymptomatic at this early stage.
The primary GI carcinoid is usually not seen on CT, but in symptomatic patients, mesenteric spread and metastatic deposits in the liver and retroperitoneal lymph nodes are frequently detectable. CT typically shows a homogenous ill defined mesenteric mass which may contain flecks of calcification. The hallmark feature is a stellate pattern of straight or curvillinear fibrosis radiating from the mass, distorting surrounding bowel loops.
History:
Figure 1: 33 year old male with diarrhea and flushing.
The single- contrast-small-bowel-follow-through study shows displacement of several small bowel loops in the midabdomen and irregularity of the small bowel mucosa compatible with a mesenteric mass infiltrating of the bowel wall.
Figure 2: The axial CT image shows a mesenteric mass associated with a desmoplastic reaction.
Figure 3: The enhanced axial CT image shows multiple subtle round lesions scattered throughout the liver parenchyma, consistent with metastasis.
Figure 4: The hepatic sonogram confirms the presence of multiple solid nodules.
DDx:
Depends on the clinical picture but lymphoma, adenocarcinoma and metastasis are in the top three.
Key references:
Sleisenger, M.H. & Fordtran, J.S. Gastrointestinal Diseases: Pathophysiologic Diagnosis and Management. 4th ed. W.B Saunders Co., Philadelphia 1989.
Kreeny, P.C. & Stevenson, G.W. Margules and Burhennes's: Alimentary Tract Radiology. 5th ed. Mosby. St. Louis, Mosby. 1194.
Laufer, I & Levine, M. S. Double Contrast Gastrointestinal Radiology. 2nd ed. W. B. Saunders Company., Philadelphia. 1992
ACR Code: