Neuroendocrine neoplasms (NENs) arise from endodermal cells These cells share common features, such as looking similar, producing biogenic amines and polypeptide hormones.[1
] Majority occur within the gastroenteropancreatic axis and are classified according to site of origin-foregut, midgut, and hind gut. They range from well-differentiated carcinoids to poorly differentiated neuroendocrine carcinomas (NECs). Staging of NENs depends on size, lymphovascular invasion, invasion of adjacent organs, and presence of metastases.[2
] Grading depends upon mitotic count and Ki67 index . Sometimes NEN include an additional significant proportion of malignant exocrine glandular cells and then it is termed as Mixed adenoneuroendocrine carcinoma of cecum (MANEC) when each component represents at least 30% of the lesion.[3
] Previously, these were termed as mixed exocrine-endocrine carcinomas. They are further classified into collision and composite types. Collision tumors are where two different histologic patterns are in close contact, and mixed or composite tumors where the endocrine and exocrine cells are intermixed within the same tumor. Composite tumors arise through multi-directional differentiation of a single neoplasm whereas collision tumors result from biclonal transformation of two separate but adjacent neoplasms.[4
] Our case was a composite tumor.
These tumors are often small, located in submucosa or intramural area and can involve the mesentery and can be firm due to desmoplastic reaction. Overlying mucosa can be intact or ulcerated. Macroscopically, these appear as polypoid masses or ulcerating stenotic lesions measuring 0.5 cm - 14 cm in diameter, with mean size of about 5 cm.
Histologically, the NEC component is morphologically similar to small cell or large cell NEC of the lung (2010 WHO classification). Immunohistochemically, pure neuroendocrine component of the mixed tumor are positive for synaptophysin and chromogranin A.[5
NENs of the gastrointestinal tract are small and difficult to detect on CT scans. Small tumors are dramatically enhancing submucosal lesions on arterial phase and its metastases to the liver enhance brightly on arterial phase imaging because of their increased vascularity,[6
] Mesenteric extension appear as ill-defined mesenteric mass containing calcification or spiculated mass with a stellate pattern. Mesenteric vessels may be involved due to desmoplastic reaction, which can lead to thickening and ischemia of the involved small-bowel as was seen in our case.
These tumors present with non-specific symptoms and are clinically occult, revealed only on exploratory surgery. They usually occur in the fifth or sixth decade of life. In many cases, diagnosis is revealed only with development of metastases. Atypical varieties show higher rate of metastasis.[4
] Any component of the mixed tumor can spread regardless of its allocation.
Because of their rarity and unusual presentation, the optimal strategy for management of mixed endocrine tumor is variable. The most contentious component of the mixed endocrine tumors must be borne in mind for alleviation of symptoms. In our case, as there were no metastases from either component at the time of scan, surgery was performed, and follow-up was advised.