[Pulmonary carcinoids and carcinoids of the small intestine]

Pulmonary carcinoids and carcinoids of the small intestine (jejunum and ileum) are often asymptomatic and can affect various parts of the body, which makes diagnosis difficult.

Contrast-enhanced computed tomography (CE-CT) is commonly used for primary diagnostics. In case of concomitant pulmonary consolidation (e.g., atelectasis or pneumonia), tumor lesions can be obscured. In addition, differentiation between atypical (AC) and typical carcinoids (TC) is not possible using CT. Small tumors of the small intestine are easily overlooked (sensitivity: 50-85%, specificity: 25-97%, based on the literature). Additional functional imaging evaluation using hybrid imaging techniques can be applied, e.g., positron emission tomography/computed tomography (PET/CT).

Depending on the histological characteristics of the tumor, PET/CT scans can be performed with different tracers. Since most carcinoids (e.g., TC) express somatostatin receptors (SSR), ⁶⁸ gallium-radiolabeled PET tracers (e.g. ⁶⁸ Ga-DOTA-TOC) are commonly used (sensitivity: 88-93%, specificity: 88-95%, based on the literature). Poorly differentiated carcinoids (e.g., AC) demonstrate lower SSR expression; thus, use of ¹⁸F‑FDG (sensitivity: 37-72%, based on the literature) is indicated. In principle, these methods enable a noninvasive prognostic differentiation based on SSR expression and ¹⁸F‑FDG uptake. However, the diagnosis must always be histologically confirmed.

Hybrid imaging with CE-CT and PET is useful to detect pulmonary carcinoids and carcinoids of the small intestine, respectively, and can be utilized for primary diagnostics and restaging.