The “spoke wheel” sign in mesenteric carcinoid

Abstract

The “spoke wheel” sign is a radiological finding described on CT images of small bowel carcinoid metastasis in the mesentery [1]. This appearance is generated by soft tissue linear stranding within the mesentery, radiating from the centrally located metastatic implant toward adjacent bowel loops, resembling a “spoke wheel” (Fig. 1) [1]. Carcinoid tumors are uncommon neuroendocrine neoplasms originating from endocrine amine precursor uptake and decarboxylation (APUD) cells. Although they can occur in any organ, approximately 60–70% of carcinoid tumors are located in the gastrointestinal tract, which has the largest reservoir of neuroendocrine cells in the body [2]. Gastrointestinal carcinoids most frequently affect the rectum (34%), followed by the small bowel (26%) [2]. On CT imaging, primary carcinoid of small intestine may be seen as small intramural masses, polypoid lesions or concentric mural thickening [2]. However, carcinoid metastasis in the mesentery may be the only imaging manifestation of a neuroendocrine tumor of the small bowel. The mesenteric involvement may manifest as enlarged lymph nodes or masses, often containing calcification, and with spiculated irregular margins, surrounded by desmoplastic reaction, configuring the “spoke wheel” pattern (Fig. 2) [3].