Update on Rectal Neuroendocrine Neoplasms

Rectal neuroendocrine neoplasms (R-NENs) are increasingly identified in clinical practice, mainly due to the expansion of colorectal cancer screening programs. These tumors are most often detected incidentally as small, well-differentiated lesions. Although many R-NENs exhibit indolent behavior, prognosis and management depend on accurate staging, with particular emphasis on evaluating regional lymph nodes and distant metastases. Cross-sectional imaging is central to this assessment. Endoscopy and endoscopic ultrasound provide essential information regarding tumor size and depth of invasion, while computed tomography (CT) and magnetic resonance imaging (MRI) are necessary for staging, risk stratification, and treatment planning. Pelvic MRI provides superior assessment of the rectal wall, mesorectum, and regional lymph nodes and is recommended for tumors measuring 10 mm or larger, higher-grade lesions, or suspected nodal involvement. CT is necessary for systemic staging, especially for detecting hepatic and extra-pelvic metastases in higher-risk tumors. This article reviews the evolving classification of rectal neuroendocrine neoplasms, describes characteristic CT and MRI findings across the disease spectrum, and discusses imaging-based criteria that guide management, surveillance strategies, and multidisciplinary decision-making. Our prior imaging-focused review addressed the role of imaging in rectal NENs; however, recent advances in cross-sectional and functional imaging, theragnostic approaches, and prognostic scoring systems warrant an updated review.