Author: Adwaita Nag (India)
Co-authors: Vikas Khetan
Purpose
Retinocytoma is a retinal tumor regarded as the benign equivalent of retinoblastoma (RB) but with the same genetic implications. Gallie et al reported a characteristic clinical triad, which, along with an absence of progression, could diagnose a retinoma: translucent retinal mass (“fish flesh”), calcific nodules (“cottage cheese”) and retinal pigment epithelial (RPE) alterations. Presence of retinocytoma is definitive evidence of the presence of the RB1 gene. This is especially important in patients with unilateral RB, normal contralateral eye and no family history of retinoblastoma. Knowledge of retinocytoma is limited due to its rarity and based mainly on clinical findings. Few histopathologic studies, performed on eyes that have been enucleated on suspicions of malignancy, reported well-differentiated features. However, there are infrequent reports of malignant transformation, highlighting the importance of regular follow-up with photographic documentation of lack of tumor growth. Advent of imaging modalities like OCT has made ‘optical biopsy’ possible, with a resolution similar to histological sections. Furthermore, OCT Angiography (OCTA) enables non-invasive visualization of the chorioretinal microvasculature within the tumour. This study aims to assess the role of multimodal imaging (MMI) in the diagnosis and monitoring of retinocytomas while attempting to gain a better understanding of these rare tumors.
Setting/Venue
This study includes patients diagnosed with retinocytoma at the Ocular Oncology Clinic of a tertiary ophthalmic institute in South India over a period of five years (2015-2020).
Methods
This was a retrospective case series including 12 retinocytomas in 11 eyes of 10 patients. The age of presentation, chief complaint, past and family history, previous misdiagnoses, laterality, best-corrected visual acuity (BCVA) were recorded. MMI including colour fundus photography (CFP), fundus autofluorescence (FAF), ultrasound B scan (USG), MRI brain and orbit, ultra-widefield (UWF) imaging, fundus fluorescein angiography (FFA), swept-source OCT (SS-OCT) and OCT Angiography (SS-OCTA) were performed. Children below 10 years of age were examined under general anesthesia and underwent Retcam imaging. The presence of the three classical features and additional features like chorioretinal atrophy (CRA), irregular blood vessels, vitreous deposits or cystic changes were documented. Size of each tumour was measured along its largest dimension in disc diameters (DD). Their location was categorized as: • Zone 1 – circle centered on foveola, including optic disc • Zone 2 – ring surrounding zone 1, extending up to posterior end of vortex veins (mid-periphery) • Zone 3 –area beyond zone 2 (far periphery) Qualitative analysis of retinal layers and choroid on SS-OCT and the superficial capillary plexus (SCP), deep capillary plexus (DCP), choriocapillaris (CC) on SS-OCTA was also performed. At each visit, the tumor was documented as stable, progressing or regressing.
Results
The median age was 11.5 years and 80% were males. A family history of retinoblastoma was present in 20%. The mean size of the retinocytomas was 6.45DD. 33.33% of tumours involved zone 1, 25% involved zone 2 and zone 3 each and 16.67% involved both zones 1 and 2. Macular involvement was present in 27.27%, optic disc in 18.18% while both were affected in 18.18%. Translucent mass was present in 66.67%, calcification in 50%, RPE disturbance in 75% and the entire triad in 50% of tumours. 66.67% had CRA. FAF revealed heterogenous pattern with iso- and hyper-autofluorescence centrally and hypo-autofluorescence peripherally. A superficial hyperreflective layer was found in 100% of eyes that underwent OCT, corresponding to the retinal nerve fibre layer (RNFL). In 50% of eyes, inner retinal layers (IRL) including ganglion cell layer (GCL), inner plexiform (IPL) and inner nuclear layer (INL) were further discernible. 66.67% had cystic spaces within the tumour, mainly in the INL. Choroidal thinning was universal. OCT angiography showed choriocapillaris loss with intact SCP and DCP. FFA showed diffuse faint hyperfluorescence with fuzzy margins and corkscrewing of overlying vessels. During a mean follow-up of 5 years, none of the tumours exhibited growth or malignant transformation.
Conlusions
This is the largest case series to date describing the MMI features of retinocytomas. On including CRA as a fourth finding, diagnostic yield increases from 50% to 66.67% for a combination of any 3 of the 4 features. Cysts have been previously suggested to be associated with increased malignant potential; in this study, cysts were seen in 66.67% of tumours but none exhibited malignant changes. Earlier studies have reported retinocytomas as featureless masses on OCT without any discernible layer. One case report identified a hyperreflective superficial layer. In this study, among tumours that underwent OCT, RNFL was identified in 100% and additional IRL in 50%. Preliminary neurosensory retinal differentiation in retinocytomas is a novel finding that has not been previously reported. It provides further evidence that retinocytomas arise de novo and are not spontaneously regressed RBs as previously believed. Retinoblastomas have full-thickness retinal replacement with disorganized tissue on OCT. Preserved retinal layers on OCT not only indicate a benign nature but can also be used to distinguish retinocytomas from RB. FFA and OCTA findings suggest intrinsic vascularity of retinocytomas. Thus MMI provides new insights into the pathology and natural history of retinocytomas and is an excellent tool for serial monitoring.
Financial Disclosure
NIL
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