Bilateral retinocytoma: multimodal imaging assessment

Abstract

Clinical evaluation of an early-onset left esotropia in an adolescent revealed a large macular lesion with extensive posterior pole retinochoroidal atrophy from superior arcade to inferior arcade. The lesion also showed pigmentary changes over the base, edges and beyond, along with a popcorn-like calcification just above the inferior arcade. Swept-source optical CT (SS-OCT) confirmed extensive chorioretinal thinning with hyper-reflective foci corresponding to the calcification, and optical CT angiography revealed a disorganised superficial retinal plexus. Likewise, fundus screening of the other eye showed a well-defined fleshy mass lesion along the temporal retina in absence of any calcification. SS-OCT of the left eye lesion showed intraretinal mass with poorly defined retinal layers.

Background

Retinocytoma or retinoma is a spontaneously arrested variant of retinoblastoma.^1–4 Clinical features of retinocytoma were first described by Gallie et al,¹ but the term retinocytoma was suggested by Margo et al ² after a detailed histopathological analysis, due to the absence of classical features of malignancy (retinoblastoma). The incidence of retinocytoma varies from 1.8% to 10% among the patients with retinoblastoma.⁴ Due to its benign nature and lesser incidence of malignant transformation, our understandings regarding this tumour are limited. Until now, most of the retinocytoma lesions were studied either clinically or on histopathology after sacrificing the eye. However, with the advent of optical CT angiography (OCTA), in vivo visualisation of these lesions is possible, which is almost equivalent to histopathological sections. Thus, herein we discuss swept-source optical CT (SS-OCT) and swept-source OCTA (SS-OCTA) features of a case of bilateral retinocytoma.

Case presentation

An 18-year-old male patient was referred to our squint clinic for esotropia in the left eye (LE) since early childhood. Birth history, medical and surgical history was insignificant. Best corrected visual acuity was 20/20 and perception of light (with an inaccurate projection of rays) in the right eye (RE) and LE, respectively. Anterior segment examination was essentially within normal limits in both the eyes. Retinal examination showed normal optic disc and the macula in the RE, whereas LE showed a large macular lesion extending from superior arcade to inferior arcade. The lesion had minimal posterior excavation with a faintly visible translucent mass lesion along the inferior portion with multiple brilliant white popcorn-like calcification at the centre. The base showed a chorioretinal atrophy with a variable pigmentary epithelial change near its boundaries. At some places, small retinal feeder vessels entering the calcified mass from the inferior arcade were noted; similarly, the bare sclera was evident with prominent overlying choroidal vessels (figure 1A).

Figure 1.

(A) Left eye fundus picture showing extensive macular involvement from superior arcade to inferior arcade with a small area of superior translucent mass and dense calcification. (B and C) B scan ultrasonography on high and low gain showing an area of well-defined posterior excavation along the posterior ocular coat with high amplitude localised spike corresponding with a calcified area. The calcified area projected postechoic shadowing along with optic nerve shadow below. (D) CT of the orbit showing an area of calcification along the posterior ocular coat in the left eye.

Ultrasonography of LE showed an area of posterior excavation having localised high amplitude spike with postechoic shadowing suggestive of calcification (figure 1B,C). Previously performed non-contrast CT confirmed the calcification (figure 1D).

On SS-OCT scanning, there was a large area of posterior ocular coat bulging, interspersed by hyperdense localised areas corresponding to the calcification (figure 2A). Within the lesion, around these calcified areas, residual featureless retinal tissue was clearly evident (figure 2A). Similarly, the choroidal tissue underneath the retina also showed diffuse thinning. OCTA with its depth-decoded abilities, imaged a disorganised superficial capillary plexus having intervening areas of dark spaces corresponding to the calcification due to signal obstruction by them (figure 2B). Presence of this calcification and scarred overlying tissue hindered the assessment of deeper retinal and choroidal plexus. In the RE, careful fundus screening revealed a small, white, fluffy mass lesion along the temporal retina (figure 2C). SSOCT of the lesion revealed a hyper-reflective homogenous intraretinal mass lesion with a distorted retinal architecture lying over a fairly defined choroid (figure 2D).

Figure 2.

(A) SSOCT of the left eye showing posterior bowing of the ocular coats with localised bright areas corresponding with the calcification. The retina layers were absent at the calcific spots, whereas along the sides, it appears thin and atrophic without any demarcation of the layers. (B) OCTA of the left eye along the superficial retinal plexus showing an intact but distorted retinal plexus with central dark areas corresponding with the calcification. (C) Left eye fundus showing a small self-regressed lesion along the temporal retina. (D) SSOCT of the left eye regressed lesion showing a well-defined homogeneous mass lesion with the layer of the retina. However, the layers of the retina could not be made out, but the underlying choroid appeared intact. OCTA, optical CT angiography; SSOCT, swept-source optical CT.

Outcome and follow-up

It was explained to the patient the nature of the disease process and was kept under close follow-up.

Discussion

Retinocytomas are usually seen in older children at around 5 years of age without any sex predilection.^3–5 These children usually do not present with leukocoria, but instead, they are diagnosed incidentally along with the retinoblastoma in the same eye or the other eye.^{4 5}

The spontaneously arrested retinoblastoma can be located at the posterior pole or along the extramacular location with varying numbers and sizes. Our patient presented with low vision and esotropia in the LE since early childhood but in absence of any elicitable history of leukocoria, even though the entire lesion occupied the posterior pole with dense calcification at the macula.

Singh et al described the common ophthalmoscopic features of retinocytoma in 17 patients in a variable proportion. The features were a translucent retinal mass lesion in 88% of the cases, calcification in 63% cases, retinal peripheral pigment epithelial alterations in 54% cases and a zone of chorioretinal atrophy in 54% of the cases. The first three clinical features together were seen in only 33% (8 out of 24) of their patients.⁴ However, the current case showed all four features, thus confirming the diagnosis of retinocytoma.

SS-OCT in our case revealed prominent thinning of the posterior ocular coat’s due to an atrophic retinochoroidal layers. Whereas the OCTA with its three-dimensional imaging capabilities showed a fairly defined superficial retinal plexus, but the deeper retinal and choroidal plexus assessment were difficult due to a greater degree of distortion and projection artefact posed by the calcification and scarred tissue.

Learning points.

• Swept-source optical CT of the retinocytoma showed an atrophic retinochoroidal layer with a correspondingly distorted superficial retinal plexus on optical CT angiography in presence of calcified lesions.

• Because of these calcifications, the assessment of outer retinal and choroidal vasculature was hindered due to projection artefacts.

• Lesion without calcification showed well-defined intraretinal mass lesion with poorly defined retinal layers.