Differentiating Sporadic and Familial Adenomatous Polyposis-Associated Congenital Hypertrophy of the Retinal Pigment Epithelium From Congenital Grouped Pigmentation: A Review of Morphologic, Histopathologic, and Multimodal Imaging.

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) occurs both as a sporadic finding and as an extraintestinal manifestation of familial adenomatous polyposis (FAP). Congenital grouped pigmentation (CGP, "bear tracks") represents a third distinct entity that may be confused with FAP-associated lesions. Accurate differentiation among these three entities has important clinical implications for appropriate surveillance, counseling, and patient management. Although prior reviews have synthesized the morphologic, histopathologic, and multimodal imaging features of pigmented retinal pigment epithelium (RPE) lesions, subsequent multimodal imaging studies and evolving evidence have refined the distinctions among FAP-associated lesions, sporadic solitary CHRPE, and CGP. This narrative review provides an updated synthesis on the clinical, fundoscopic, optical coherence tomography (OCT), fundus autofluorescence (FAF), OCT angiography (OCTA), and histopathologic features of FAP-associated CHRPE, sporadic solitary CHRPE, and CGP. Key differentiating features of FAP-associated lesions include multiplicity, bilaterality, absence of lacunae, absence of cystoid edema, and presence of pigment epithelial detachments (PEDs). CGP is distinguished by its wedge-shaped (sectorial) distribution pattern, preserved outer retinal architecture on OCT, and retention of normal ellipsoidal pigment granule morphology on histopathology. An evidence-based diagnostic feature comparison framework is proposed to assist clinicians in determining which patients with pigmented RPE lesions warrant genetic evaluation for FAP.