Multimodal imaging in choroidal osteoma

Purpose To describe characteristics of choroidal osteomas (CO), using ocular ultrasound, fluorescein angiography, ultra-widefield retinal imaging, ultra-widefield autofluorescence, optical coherence tomography, enhanced-depth-imaging OCT, and OCT angiography (OCT-A). Methods Retrospective, observational case series study. Clinical records from patients with diagnosis of CO who underwent complete imaging evaluation were analyzed. Results Sixteen eyes from 11 patients were included. Mean patient age was 33.4 years (range 20–61), 72.7% were female, 100% were Hispanic, and 54.5% had unilateral CO. Median visual acuity was 20/150 (range 20/20–2000). CO was completely calcified in 25%, partially decalcified in 50%, and decalcified in 25%. Other features included choroidal neovascularization (18.75%), focal choroidal excavation (12.5%), choroidal depression associated to decalcification (18.75%), thinning of outer retina and photoreceptor layers over decalcified tumor (75%). Decreased fluorescence on FAF was observed in decalcified regions while relatively preserved fluorescence was observed in calcified regions. Conclusions Nowadays, diagnostic tests provide important information about each stage of choroidal osteoma. Progressive decalcification of the tumor might have a common pathogenic role for development of FCE or choroidal depression. OCT-A/FA proved to be valuable tools for detection of CNV in patients with CO.


Introduction
Choroidal osteoma (CO) is a rare benign tumor of the choroid, which is composed of mature bone (trabecular and/or compact) and vascular channels [1][2][3][4]. Gass et al. made the first description of this kind of neoplasm in 1978, and since then multiple case reports and series have been published [5].
CO is typically unilateral (80% of cases) and it usually affects young healthy female patients [6]. It arises in late childhood or early adulthood and its most common symptoms are blurred vision, metamorphopsia and presence of a scotoma [7]. The clinical appearance of the tumor may vary from white-cream or yellow-gray to orange, well-defined, which according to some authors corresponds to the grade of calcification (orange pigmentation is present in areas with more ossification) [6].
Over time, ocular ultrasound (US), fluorescein angiography (FA) and optical coherence tomography (OCT) have been widely used for diagnosis and follow-up of CO. Enhanced depth imaging OCT (EDI-OCT) is a recent addition of OCT, that has been able to reveal the presence of bone lamella, tubular lamella with optically empty center, vascular channels and trabecular bone in patients with CO [8,9].
In patients with CO, OCT angiography (OCT-A) is a new non-invasive imaging technique that employs motion contrast from blood flow to generate high-resolution angiographic images, in patients with CO has been able to show a dense irregular vascular network in the outer retinal layer (ORL) and choroid capillary layers [10]. On the other hand OCT-A [11].
The aim of this study is to describe the morphology of CO using a multimodal image system.

Methods
The clinical records of patients with a diagnosis of choroidal osteoma who had undergone multimodal fundus imaging on the retina service at Asociación para Evitar la Ceguera en México were reviewed. The diagnosis was based on the presence of a yellow-white to orange-red mass deep to the RPE and bone density on ultrasonography. Institutional review board approval was obtained for this retrospective study.
Multimodal imaging analysis included ultrasonography (US), fluorescein angiography (FA), ultra-widefield retinal imaging (UWF), ultra-widefield autofluorescence (UWF-FAF), optical coherence tomography (OCT) and OCT angiography (OCT-A). Enhanced depth imaging optical coherence tomography (Spectralis HRA + OCT; Heidelberg Engineering, Germany), data included tumor surface configuration (flat or depressed), effects of tumor on overlying retina (RPE, photoreceptor and inner retina status). One independent physician manually measured osteoma thickness with a caliper function through the epicenter of the tumor.
Fluorescein angiography (FA) (Spectralis HRA + OCT; Heidelberg Engineering, Germany) data included presence or absence of CNV. OCT-A images were analyzed in patients in whom FA was performed and correlated with

Results
There were 16 eyes in 11 patients with choroidal osteoma included in this study. The demographic and clinical characteristics are summarized in Table 1. All patients were Hispanic and diagnosis corresponded to primary CO in 15 eyes, whereas one patient had CO secondary to choroidal hemangioma. The median age at presentation was 33.4 years (range 20-61 years). Most patients were female (72.7%).

Discussion
Choroidal osteomas may demonstrate decalcification, CNV, retinal pigment epithelium (RPE) alterations and vision loss [6]. Patients with calcified areas, even subfoveolar ones, had better visual acuities; while patients with decalcified CO had lower visual acuities correlated with RPE disruption and outer layer thinning and photoreceptor loss, and corresponded to hypo-AF on AF [8,12]. Table 1. In our series two eyes (12.5%) presented CNV in the proximity of focal choroidal excavation (FCE) Fig. 1. Margolis et al. [13] described the FCE in conforming lesions, in which the overlying retina is close to the RPE, and nonconforming lesions in which a hypo reflective space is visible between the retina and RPE, in our series one patient had conforming and the other one had nonconforming FCE. Pierro et al. [14] described in two patients with CO the presence of CNV and FCE. CE has an increased separation between retinal pigment epithelium and neurosensory retina without schisis of the corresponding retinal layers; the location is in correspondence or in proximity of the tumor. In our series three eyes had choroidal depression associated with tumor decalcification Fig. 2. This feature is characterized by intrinsic hyperreflective dots within tumor (speckled regions) in the proximity of choroidal depression, neurosensory retina may show schisis, this depression is not always associated with CNV. FCE and choroidal depression may represent distinct stages of focal decalcification of the tumor, this hypothesis is supported by the fact that we were able to follow one patient that developed choroidal concavity, situation that allowed us to see that this depression can grow overtime (Fig. 3).

Conclusions
Choroidal osteoma is an ossifying tumor involving the choroid, its natural course may include tumor growth, calcification and decalcification; visual acuity depends on choroidal neovascularization and retinal changes associated to decalcification [12]. Duration of this condition is a mayor risk factor associated with vision loss. After 10 years, approximately 51% manifest evidence of growth and nearly 50% showed decalcification. Calcified and decalcified areas have demonstrated changes in outer retina. Optical coherence tomography changes have been shown that calcified areas have intact outer retina whereas decalcified portion have thinned to absent outer retina and photoreceptor layers [12].
In our series, the mean age at diagnosis was 33 years and females represented 72.7%, however 45.5% of our patients were bilateral, this patients showed osteomas located in the macular area with extension beyond the vascular arcades and showed RPE alterations due to osteoma decalcification.
Patients witth CNV whose medical records had FA and OCT-A also where evaluated, both have good correlation in determining the site of neovascularization.