Choroidal osteoma is a benign osseous choristoma in which mature bone tissue forms in the choroid. It is characterized by replacement of the choroidal stroma with mature bone.
It was first reported at the 1975 Verhoeff Society meeting. A 26-year-old woman with a paracentral scotoma presented with a yellowish-white subretinal tumor on the nasal side of the optic disc in the left eye. It commonly occurs in the posterior pole of young women in their 10s to 30s. It is usually unilateral, but about 20% of cases are bilateral.
It is a rare tumor, with only 61 cases reported over 26 years at a tertiary medical center. Significant vision loss can occur in about 60% of affected eyes. 1) It has also been reported that up to 90% of ophthalmologists miss it on initial examination. 1)
Fundus findings are characterized by a well-defined, map-like, yellowish-white to orange, flat lesion located in the posterior pole. Over time, pigmentation, RPE atrophy, and decalcification occur, changing the fundus appearance. The lesion gradually enlarges but eventually stops.
Malignant transformation has not been reported; it is essentially a benign tumor. However, secondary choroidal neovascularization can significantly reduce vision. For details, see the section on “Standard Treatment”.
Symptoms vary depending on the tumor location, size, and presence of complications.
The following findings are observed in the posterior pole of the fundus, especially around the optic disc.
The cause of choroidal osteoma is unknown. Several hypotheses have been proposed regarding why ectopic bone formation occurs in the choroid, but no definitive factor has been identified.
Proposed contributing factors are listed below.
Genetic factors are suggested to be involved, but a definitive inheritance pattern has not been identified. Although there are reports of family history, it is not established as a hereditary disease.
Diagnosis is primarily clinical. 1) A combination of multimodal imaging assessments is important for definitive diagnosis. 1)
Ultrasound is a particularly useful examination. 1)
High-reflectivity lines are observed within the choroid. 1) It is also useful for evaluating photoreceptor atrophy, choroidal compression, and subretinal fluid. OCT angiography (OCTA) is useful for detecting choroidal neovascularization.
A high-attenuation area equivalent to bone is depicted corresponding to the tumor. This is the most specific test leading to a definitive diagnosis and is useful for differentiating from other choroidal masses.
Both T1- and T2-weighted images show low signal intensity. This finding reflects the characteristics of bone tissue.
The main diseases requiring differential diagnosis are listed below.
| Disease | Color | Morphological Features |
|---|---|---|
| Malignant melanoma | Black to gray to brown | Elevated lesion with height |
| Choroidal hemangioma | Orange-red | Fusiform |
| Metastatic tumor | Yellow-white | Plate-like, flat |
Additionally, differentiation from sclerochoroidal calcification and amelanotic melanoma is necessary. Acoustic shadowing on B-mode ultrasound and bone density confirmation on CT are decisive for differentiation. 1)
Machado et al. (2024) reported two atypical cases, one misdiagnosed as age-related macular degeneration and the other as choroidal hemangioma. 1) Both were diagnosed as choroidal osteoma by ultrasound and OCT.
Diagnosis is often possible by combining clinical findings with ultrasound and OCT. CT is useful for definitive diagnosis by showing high absorption areas similar to bone, but it is not mandatory in all cases. It is particularly helpful in difficult-to-diagnose cases or when differentiation from other choroidal tumors is needed.
There is no fundamental cure. The management strategy depends on the lesion status and presence of complications.
Observation
Indications: Asymptomatic or stable lesions. No choroidal neovascularization.
Plan: Continue regular follow-up with fundus examination, OCT, and visual acuity measurement.
Note: If you experience changes in vision, metamorphopsia, or blurred vision, you should see a doctor promptly. Early detection of new choroidal neovascularization is important.
Treatment for Choroidal Neovascularization
Intravitreal anti-VEGF injection: Bevacizumab and ranibizumab are used. 1) This aims to resolve subretinal fluid and hemorrhage associated with choroidal neovascularization.
Photodynamic therapy (PDT): A spot size of 6,000 μm is standard; multiple sessions may be given for large tumors. It minimizes retinal damage while also expecting tumor regression.
Laser photocoagulation: May be used as an adjunctive treatment for choroidal neovascularization.
Considered as first-line treatment when choroidal neovascularization is present. Bevacizumab (Avastin) and ranibizumab are used. 1) The goal is to resolve subretinal fluid and hemorrhage associated with choroidal neovascularization. Both are off-label treatments for choroidal osteoma.
The protocol based on the TAP study is used as a reference. A spot size of 6,000 μm is standard, and multiple sessions may be performed for large tumors. PDT allows treatment of the lesion while minimizing damage to the surrounding retina, and is expected to induce regression of the tumor itself. In Japan, PDT for choroidal osteoma is an off-label treatment.
Used as an adjunctive treatment for choroidal neovascularization. It may be considered for extrafoveal choroidal neovascularization.
If bullous retinal detachment occurs over the tumor, vitrectomy with subretinal fluid drainage and intraoperative laser photocoagulation may be performed.
For asymptomatic and stable lesions, observation is the basic policy. However, if choroidal neovascularization occurs, vision loss may progress rapidly, requiring prompt treatment intervention. It is important to continue regular ophthalmologic examinations and watch for the appearance of new symptoms.
Choroidal osteoma is classified as a congenital osseous choristoma. It is characterized histologically by the replacement of choroidal stroma with mature bone.
Histologically, mature bone tissue is observed. The marrow spaces are filled with loose connective tissue and dilated thin-walled vessels. The marrow vessels communicate with the sub-Bruch’s membrane capillary network and degenerated RPE.
Tumors commonly occur adjacent to or around the optic disc and can extend to the macula. The lesion gradually expands peripherally but tends to eventually stop.
Visual impairment occurs mainly through the following mechanisms.
Decalcification occurs naturally but can also happen after laser photocoagulation or PDT. It is observed on the fundus as a thinned, atrophic yellowish-gray area of the tumor. At the advancing edge of decalcification, tumor enlargement tends to stop, which may be associated with scar stabilization of the tumor.
Long-term follow-up studies have accumulated the following prognostic data.
| Outcome Measure | Frequency at 10 Years |
|---|---|
| Visual acuity 20/200 or worse | 56–58% |
| Tumor enlargement | 41–51% |
| Choroidal neovascularization | 31–47% |
| Calcification | 46% |
The average tumor growth rate is reported to be approximately 0.37 mm per year. Long-term poor vision is associated with subretinal fluid, RPE changes, and subretinal hemorrhage from choroidal neovascularization. Progression of decalcification is also a predictor of poor vision.
For extrafoveal calcified osteomas, a strategy has been proposed to prevent tumor enlargement by decalcifying the tumor margin using PDT. This is based on the observation that tumor growth does not occur in areas where decalcification has progressed. However, prospective studies to prove the effectiveness of this treatment strategy are still limited.
In a report of two atypical cases by Machado et al. (2024), choroidal osteoma was misdiagnosed as age-related macular degeneration and choroidal hemangioma. 1) In one case, an irregular lesion in the posterior pole was treated as age-related macular degeneration, and in the other, an orange-red fundus finding was misdiagnosed as hemangioma. Acoustic shadowing on B-mode ultrasound and identification of high-reflective lines within the choroid on OCT are key to improving diagnostic accuracy.
Based on reports that up to 90% of ophthalmologists miss the diagnosis at the initial visit 1), the importance of including this disease in the differential diagnosis for posterior pole lesions in young women is being reaffirmed. The widespread use of multimodal imaging is expected to contribute to improved diagnostic accuracy.
