Diagnosis of an isolated retinal astrocytic hamartoma aided by optical coherence tomography

Abstract

An otherwise healthy 15-year-old girl was referred for evaluation of a retinal tumour in her left eye. Her visual acuity was 20/20 bilaterally. A solitary translucent retinal tumour measuring 1.5 × 3.0 disc diameters was seen inferior to the optic disc (Fig. 1A). The retinal arteries passing through the tumour appeared white. The sensitivity over the tumour was not altered in Humphrey visual field tests (Fig. 1B). Fluorescein fundus angiography (FA) showed retinal circulation to be intact with only weak staining of a section of the tumour (Fig. 1C,D). An ultrasound B-mode echography showed a mass inferior to the optic disc; no calcifications were observed (Fig. 1E). (A) A retinal astrocytic hamartoma is seen as a translucent mass below the optic disc. (B) Humphrey visual field shows no close-to-normal retinal sensitivity loss over the area of the tumour. (C) Fluorescein angiogram 35 seconds after injection shows intact retinal circulation and (D) 12 min after injection shows slight staining of a small part of the tumour. (E) Ultrasound echography of vertical section shows a high reflectivity mass inferior to the optic disc without back shadow. (F) The retinal nerve fibre layer is thickened by the tumour. The retinal ganglion cell (RGC), inner and outer plexiform (IPL and OPL) and nuclear layers (INL and ONL), the border of inner and outer segments (IS/OS) and retinal pigment epithelium (RPE) of normal architecture are also imaged. A focal adhesion of the posterior vitreous cortex is visible; it appears to exert traction to the surface of the tumour (asterisk in F–H). The surface of the retina has a mulberry-like appearance. Inset shows an orientation scheme for optical coherence tomography (OCT). The blue square indicates the 6.0 × 6.0 mm scanning area, and the yellow and light blue lines indicate the scanning planes corresponding to F and G, respectively. (G) Retinal arteries (a) passing through the tumour have walls of high reflectivity and show back shadowing, while the veins (v) are indiscernible. (H) Three-dimensional imaging highlights the architecture and relationship of the tumour and surrounding tissues (S, superior; T, temporal; I, inferior). The fundus was scanned with optical coherence tomography (OCT) (3D OCT-1000; Topcon, Tokyo, Japan). The measurement beam was focused on the macular area with a system based on a conventional spectrometer-based Fourier-domain OCT (FD-OCT). A three-dimensional data set was acquired using the default setting of 512 × 128 raster scan protocol. With this protocol, the beam scanned a 6.0 × 6.0 mm area of the fundus at a depth of 4.0 mm, rendering horizontal pixel spacings of 11.7 μm with vertical pixel spacings of 46.9 μm. The OCT images revealed a retinal tumour localized within the nerve fibre layer (NFL) with the outer retinal layers intact (Fig. 1F). The retinal vessels were clearly seen passing through the tumour (Fig. 1G), and the walls of the artery had high reflectivity while that of the vein were indiscernible. The outer retinal layers from the retinal ganglion cell layer to the retinal pigment epithelium (RPE) layer were clearly imaged and intact. Part of the posterior vitreous cortex appeared to exert a strong tractional force on the surface of the tumour, giving the retina a mulberry-like appearance (Fig. 1G,H). The tumour was diagnosed as an astrocytic hamartoma. The parents and older brother of the patient had no remarkable findings; unilateral astrocytic hamartomas are occasionally seen close to the optic disc in patients with tuberous sclerosis (Shields 1999). However, a solitary astrocytic hamartoma can also be seen in otherwise healthy patients. Ophthalmoscopically, an astrocytic hamartoma is typically white, well-circumscribed and elevated, and is found most commonly in the peripapillary area (Shields 1999). They may gradually calcify but generally they do not enlarge, and symptomatic progression is very rare. Our case was of uncalcified type and thus of type I according to the classification by Rowley et al. (2001). The translucency of the retina as well as the intact retinal layers – except the NFL where the tumour was located – explained the minimal functional changes revealed by visual field testing in our case. Improved in vivo resolution of OCT instruments has increased the ability of clinicians to make more accurate diagnoses and to obtain a better understanding of the pathology of retinal diseases, including tumours (Shields et al. 2006). Soliman et al. (2007) imaged an uncalcified astrocytic tumour, and reported that the underlying neurosensory retina and RPE were structurally normal, a finding that was confirmed by histopathology. In our patient, only subtle shadowing of the tissues under the tumour was observed in spite of its high reflectivity, which was possibly because of the translucency of the tumour. The selective whitening and high reflectivity of the arterial wall in the tumour might be caused by calcification. Retinal astrocytic hamartomas should be followed because the tumour might grow to develop an exudative retinal detachment or epimacular membrane (though not frequently) (Mennel et al. 2007). A localized vitreous traction on the surface of the tumour was evident in our case; mild retinal traction on the surface of astrocytic hamartomas is noted in 27% of cases (Shields et al. 2006). The surface of the tumour was irregular, giving it a mulberry-like appearance even though it was neither a deep lesion nor calcified. The region where the surface was irregular corresponded to the region of the vitreous traction. The high-resolution OCT, in combination with other standard ophthalmic examinations, may be a valuable tool to monitor the progress of retinal tumours and to clarify the mechanism of secondary changes around the tumour. Support for this study was provided by Research Grants on Sensory and Communicative Disorders from the Ministry of Health, Labour and Welfare, Japan.