Optical Coherence Tomography of Small Retinoblastoma.

PURPOSE: To investigate hand-held optical coherence tomography (HH-OCT) characteristics of small (<1 mm thickness) retinoblastoma.

DESIGN: Retrospective observational case series.

METHODS: Patient and tumor data were extracted from the medical record and analyzed along with HH-OCT scans. Determination of tumor layer of origin was performed using a layer-by-layer analysis of HH-OCT data and specific HH-OCT-related features were described.

RESULTS: There were 20 sub-millimeter retinoblastomas from 16 eyes of 15 patients. Mean largest tumor basal diameter by HH-OCT was 2.2 mm (median, 1.9; range, 0.7-4.1 mm), and mean tumor thickness was 468 μm (median, 441; range, 151-998 μm). In all cases, the retinoblastoma caused discontinuity or disruption of the inner nuclear (INL), outer plexiform (OPL), outer nuclear (ONL), and external limiting membrane (ELM) layers (20/20, 100%). Tumor origin was in the INL in 19/20 (95%) and equivocal (INL vs ONL) in 1/20 (5%). Intratumoral microcalcification was present in 14/20 tumors (70%). There were 2 characteristic findings (signs) on HH-OCT including the INL "fish tail" sign with splaying of the INL at the tumor margin (19/20, 95%) and the ONL "shark fin" sign with folding of the ONL and OPL, conforming to the lateral tumor margins (15/20, 75%). Both signs were concurrently present in 15 tumors (15/20, 75%).

CONCLUSIONS: HH-OCT demonstrated that sub-millimeter retinoblastoma seems to originate from the INL, with tumor base and thickness growth progressing in a linear relationship. Characteristic HH-OCT findings included intratumoral microcalcification, INL "fish tail" sign, and ONL "shark fin" sign.