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Acute appendicitis: a surprising finding

Clinical Presentation
A 14-year-old boy with no significant past medical history presented to the emergency department complaining of severe abdominal pain which had begun several hours prior in a periumbilical location, then had migrated to the right lower quadrant. Physical examination revealed marked right lower quadrant abdominal tenderness, and a complete blood count was remarkable for a leukocyte count of 13,300/µL. A CT scan of the abdomen revealed an enlarged appendix with thickened walls. The patient was taken to the operating room and an appendectomy was performed.

Pathological Findings
Gross examination of the appendectomy specimen revealed marked diffuse erythema and edema of the appendix and mesoappendix. The lumen was filled with a thick, purulent exudate that focally appeared to extend through the wall, coating the serosal surface of the specimen. Representative sections were submitted. Microscopic examination of representative sections of the appendix revealed an intramural neoplasm.

Diagnoses
Carcinoid tumor
Acute appendicitis with transmural necrosis and serositis

Discussion
Carcinoid tumor is the most common tumor of the appendix, and is found in approximately 1 of 300 routine appendectomy specimens. They may appear in any age group, but are most common in adults. In some cases, the tumor is found in the setting of acute appendicitis, presumably as a result of luminal obstruction. Appendiceal carcinoids frequently arise in the appendiceal tip, which can result in a typical “bell-clapper” appearance. The carcinoid syndrome, which includes vasomotor disturbances, intestinal hypermotility, and sometimes systemic fibrosis, is presumed to occur as the result of excess production of 5-HT by tumor cells. In the absence of liver metastases, the syndrome is rare in appendiceal carcinoids, as the liver degrades 5-HT to the functionally inactive 5-HIAA before it enters the systemic circulation.^1,2

Several histological variants are recognized. As seen in this case, the classic type is comprised of tumor cells with minimal atypia, which form small nests and occasional acinar formations or rosettes. The tubular (adenocarcinoid) type displays a prominent glandular architecture, and can be misdiagnosed as adenocarcinoma. The less common goblet cell (mucinous) types are characterized by signet ring cells, which may form nests or glandular structures. In all three types, a predominantly submucosal growth pattern is typical, and invasion of muscle and lymphatic vessels is extremely common. The tumor cells are usually immunohistochemically reactive for synaptophysin, chromogranin, neuron-specific enolase, 5-HT, and other less commonly used markers. Most appendiceal carcinoid tumors, especially those less than 2 cm in diameter, behave in an indolent fashion and rarely metastasize, though the mucinous types are considered more aggressive. Appendectomy is generally considered adequate treatment for tumors less than 1 cm in diameter, with right hemicolectomy reserved for tumors greater than 2 cm in diameter.^1,3

In this case, re-examination of the specimen never revealed any grossly discernible tumor. The entire appendix was submitted for microscopic examination, and tumor was only seen in two of twelve slides. The fact that this small tumor was discovered only serendipitously invites speculation about the frequently at which such tumors may escape detection altogether, and raises questions about the natural history of these small lesions.

1. Rosai J, Ackerman LV. Rosai and Ackerman’s Surgical Pathology. 9th ed. Edinburgh ; New York: Mosby 2004.
2. Kumar V, Abbas A, Fausto N. Robbins and Cotran Pathologic Basis of Disease, 7^th ed. 2007. Elsevier.
3. Goede AC, Caplin ME, Winslet MC. Carcinoid tumor of the appendix. Br J Surg. 2003 Nov;90(11):1317-22.