Optical coherence tomography features of atypical congenital hypertrophy of the retinal pigment epithelium associated with colonic polyposis

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) are rare benign congenital hamartomas of the retinal pigment epithelium (RPE). They are asymptomatic lesions and are detected incidentally on routine ophthalmoscopy. Three variants of CHRPE are recognized based on the number and distribution – solitary, grouped, and atypical. Atypical CHRPEs are multifocal and usually bilateral. They are oval lesions and have a tapering tail. Solitary and grouped variants are not associated with ocular or systemic issues, whereas atypical variants are more commonly associated with syndromes known to cause colonic polyps and colonic adenocarcinoma. Identification of atypical CHRPE serves as a specific screening marker for familial adenomatous polyposis (FAP).[1] Previous studies have described histopathological and optical coherence tomography (OCT) features of solitary CHRPE. We discuss details of two patients who had atypical CHRPE with slightly different morphology of CHRPE lesions with an emphasis on the OCT appearance.

Case 1

A 49-year-old male, a case of colonic polyposis planned for surgical resection, was referred from surgical gastroenterology for fundus examination. His best-corrected visual acuity (BCVA) was 20/20 in both eyes. Fundus examination of the left eye showed two large tadpole-shaped lesions close to the posterior pole with a hyperpigmented body and a hypopigmented tail pointing toward the disc. They also had a fine hypopigmented ring around the body. Four similar small lesions were seen in the mid-periphery of the right eye. Based on the appearance, a diagnosis of atypical CHRPE was made. He was diagnosed to have colonic polyposis with synchronous carcinoma of the colon on colonoscopy-guided biopsy. The patient underwent total proctocolectomy where the cut section revealed numerous polyps (>100) throughout the colon and rectum.

Case 2

A 34-year-old male, a case of multiple colonic adenomas with carcinoma colon with hepatoblastoma was referred for fundus examination. His BCVA was 20/20 in both eyes. The right eye fundus showed about eight spindle-shaped lesions [Figures 1 and 2]. Moreover, the left eye had four such lesions. Most lesions had a hyperpigmented body and a surrounding hypopigmented ring. Few lesions had a reversal of this appearance – hypopigmented body and hyperpigmented ring. Lesions were consistent with atypical CHRPE. The patient underwent proctocolectomy and histopathology revealed adenocarcinoma in the background of polyposis.

Figure 1.

Montage color fundus photograph of the patient's right eye showing well-defined hyperpigmented lesion (CHRPE) marked by a black pointed arrow

Figure 2.

Montage color fundus photograph of the patient's left eye showing multiple well-defined hyperpigmented lesions (CHRPE) marked by a black pointed arrow

Optical coherence tomography features

Spectral-domain OCT scan through the lesions was performed in both patients. Pigmented areas of the lesions showed irregular, thicker and hyperreflective RPE, whereas hypopigmented areas showed a complete absence of RPE but an intact Bruch membrane. Both hypopigmented and hyperpigmented areas showed the absence of outer retinal layers. The inner layers were variably disorganized, dipping directly onto the choroid [Figure 3]. There was shadowing of the choroid in scans corresponding to pigmented areas. Hypopigmented areas showed increased transmission onto choroid. Except for the attenuation of choriocapillaris, other layers of choroid appeared intact.

Figure 3.

OCT image of the patient at the lesion section showing irregular, thicker, and hyperreflective retinal pigment epithelium (RPE), whereas hypopigmented areas showed a complete absence of RPE but an intact Bruch membrane marked by a yellow pointed arrow

The presence of ≥3 atypical CHRPE lesions in one or both eyes is a specific phenotypic marker for FAP.[1] They are true congenital lesions and share a common mutation in the APC gene (5q21-22) with colonic polyposis.

Histologically, solitary CHRPE lesions reveal a single layer of hypertrophied RPE cells with large pigment granules.[2] Atypical CHRPE lesions, in addition to hypertrophy, also show hyperplasia with increased pigment granules.[3] They presumed that the abnormal FAP gene, which causes colonic polyps and soft-tissue tumors is also responsible for defective melanogenesis and focal lesions of RPE.

On OCT, solitary CHRPEs appear as flat lesions with absent, thickened, or irregular RPE and the overlying retina shows thinning or absence of outer retina and occasional subretinal cleft.[3,4] In our patients, atypical CHRPE lesions demonstrated hyperreflective RPE with absent outer retinal layers and disorganized inner layers. Sagar et al.[5] showed that these lesions have hyperreflective thickened RPE with loss of outer retinal layers. They also noted intraretinal hyperreflectivity, possibly due to intraretinal RPE migration, as suggested by Traboulsi et al. However, in both patients, intraretinal hyperreflectivity was not noted in any of the scans. It is also interesting to note that these lesions uniformly showed the absence of an outer retina with a disorganized inner retina. It is suggested that the hypertrophied RPE cells, which lack phagocytic activity, leads to secondary degeneration of the adjacent retina.

We describe OCT features of atypical CHRPE lesions associated with colonic polyposis. The RPE layer was irregular, thicker, and hyperreflective, with absent outer retinal layers and an intact Bruch membrane. Inner layers were disorganized and dipping into the choroid. Hypopigmented areas showed the absence of RPE with similar retinal features.

Ethical approval

A written informed consent form was obtained from the patient.

Declaration of patient consent

The authors certify we have obtained appropriate patient consent forms. The patient has given their consent and other clinical information to be reported in the journal in the forms. The patient understands that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.