Choroidal osteoma (CO), also known as osseous choristoma, is a rare benign osseous tumour of the choroid. It is diagnosed based on the presence of a yellowish-white to orange lesion deep in the retinal pigment epithelium (RPE) with well-defined margins and bone density in ultrasonography (Pellegrini et al. 2014). Patients are usually asymptomatic and the lesion is found incidentally. Choroidal neovascularization (CNV) is the most frequent complication of CO and leads to severe visual impairment. Anti-vascular endothelial growth factor (Anti-VEGF) therapy has been recommended for CNV-related CO (Song & Roh 2009). Here, we report a case of extrafoveal CO associated with CNV. A 75-year-old woman, incidentally diagnosed with CO at the age of 68 years, presented with a two-month history of metamorphopsia in the left eye. Best-corrected visual acuity (BCVA) was 0 logMar in the right eye and 0.7 logMar in the left eye. Anterior segment findings were unremarkable in both eyes. A fundus examination of the right eye was unremarkable, whereas, in the left eye, it revealed a yellowish-white area with small haemorrhages in the superior temporal retina that suggested an extrafoveal CO associated with CNV (Fig. 1A,B). Baseline evaluation of the right eye. (A, B) Colour fundus photography and multicolour image showing the choroidal osteoma with subretinal haemorrhage. The black circle underlines macular haemorrhage spots. (C−E) Optical coherence tomography (OCT) angiography, fluorescein angiography and indocyanine green angiography revealed late-stage choroidal neovascularization within the tumour. The red circle underlines macular haemorrhage spots (F, G) A and B scan echography showed a slightly elevated choroidal mass with high reflectivity and acoustic shadowing. (H) Enhanced depth imaging optical coherence tomography (EDI-OCT) showed a hyper-reflective mass in the subretinal space associated with a neurosensory detachment and detected a sponge-like structure of the choroid. (I, J) Fluorescein and indocyanine angiography of the superotemporal region of the contralateral normal eye. (K) Optical coherence tomography (OCT) scan of the macular region without any pathological feature. (L−P) Colour fundus photography, multicolour image, fluorescein angiography and indocyanine green angiography and OCT angiography showing regression of the choroidal neovascularization after four months of treatment. (Q) Enhanced depth imaging optical coherence tomography (EDI-OCT) revealed resolution of the subretinal fluid. [Correction added on 17 June 2016 after first online publication: Figure 1 has been replaced to correct the labelling of Fig. 1E and 1O]. Optical coherence tomography (OCT) angiography (angiovue software RTVue; Optovue Inc., Fremont, CA, USA) showed a hyporeflective area surrounded by a hyper-reflective-edged ring in direct relation to the osteoma. It also showed a dense irregular vascular network within the tumour in the outer retinal layer and choroid capillary layers. Moreover, the CNV detected in the choroidal layer had fine glomerular-like hyper-reflection (Fig. 1C). Visualization of vessels is better with non-invasive OCT angiography than with fluorescein angiography (FA) and Indocyanine green angiography (ICGA); in fact, with the latter two techniques, the leaking vessels of the CNV usually are overshadowed by the dye in the late phases (Wang et al. 2015). Fluorescein angiography (FA) showed early hyperfluorescence due to leakage surrounded by an area of blocked fluorescence, and late staining of the lesion showed well-defined borders (Fig. 1D). Indocyanine green angiography (ICGA) confirmed the presence of an active CNV secondary to CO (Fig. 1E). Standardized A and B scan echography revealed a slightly elevated choroidal mass with high reflectivity and acoustic shadowing (Fig. 1F,G). Enhanced depth imaging optical coherence tomography (EDI-OCT) performed with the Heidelberg Spectralis HRA + OCT (Heidelberg Engineering, Heidelberg, Germany) showed a hyper-reflective mass in the subretinal space associated with neurosensory detachment and elongation of the outer segments. Enhanced depth imaging optical coherence tomography (EDI-OCT) also revealed a sponge-like structure of the choroid with horizontal tubules (Fig. 1H). The findings obtained in our patient strongly support the diagnosis of OC as opposed to sclerochroidal calcification (SCC). In fact, unlike OC, SCC does not feature growth, decalcification or intralesional vessels of CNV, as recently reported by Shields et al. (2015). After obtaining informed consent, we administered three monthly intravitreal injections of ranibizumab in the left eye. Four months later, the patient's BCVA was 0.1 logMar, and a fundus examination revealed resolution of the subretinal haemorrhage (Fig. 1L,M). Fluorescein angiography (FA) and ICGA showed regression of the CNV (Fig. 1N,O) and spectral domain OCT revealed no subretinal fluid (Fig. 1Q). Optical coherence tomography (OCT) angiography demonstrated a smaller and more rarified vascular network inside a capsular formation (Fig. 1P). These findings remained unchanged during the 12-month follow-up. In summary, OCT angiography reveals unique features in the vascular changes of CNV in CO not visualized with other imaging methods. However, additional studies are needed to verify whether this technique can partially replace FA and ICGA in the diagnosis and follow-up of CNV secondary to CO.

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