CHOROIDAL OSTEOMA

Choroidal osteoma is a benign, ossifying tumor of the choroid, with a distinct clinical and histopathologic appearance. These tumors are found most commonly in young women but can also be seen in other patients. Choroidal osteomas are frequently unilateral, but can also be bilateral. No family history is found in most patients.

Symptoms

Metamorphopsia, scotoma, and blurred vision may be due to direct tumor involvement of the macula, or more commonly to choroidal neovascularization.

Clinical Features

Ophthalmoscopic examination usually reveals a relatively thin, plaque-like, yellow-tan lesion with sharp, scalloped borders. The tumors usually arise adjacent to the optic nerve and may increase slightly in size on serial examination. However, they have no malignant potential. The most common cause of visual loss is choroidal neovascularization, which often occurs on the temporal margin of the tumor and may produce subretinal fluid, lipid, or hemorrhage into fixation.

Ancillary Testing

B-scan ultrasonography shows a highly reflective, plaque-like structure at the level of the choroid that persists as a strong signal when the gain is reduced to a level where other ocular structures can no longer be seen. Similarly, computed tomography shows a strong signal indicating calcium within the lesion. Fluorescein angiography reveals early hyperfluorescence with late staining of the osteoma. Fluorescein angiography also can be helpful in demonstrating choroidal neovascularization.

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Pathology/Pathogenesis

The pathogenesis of choroidal osteomas is unknown. Choroidal osteomas are composed of mature bone elements within the choroid, including osteoblasts, osteoclasts, osteocytes, and a calcium-containing matrix.

Treatment/Prognosis

Laser photocoagulation may be indicated for treatment of choroidal neovascularization. The role of photodynamic therapy for choroidal neovascularization

in patients with choroidal osteomas is unclear.

Systemic Evaluation

No consistent systemic abnormalities have been associated with choroidal osteoma, although a simulating lesion, sclerochoroidal calcification, can be associated with hyperparathyroidism, chronic renal failure, and other abnormalities in calcium and phosphorus metabolism.

Fundus photograph of a thin, plaque-like, peripapillary tumor with scalloped borders consistent with a choroidal osteoma.

Fluorescein angiogram of the same patient demonstrates irregular hyperfluorescence as a result of retinal pigment epithelial atrophy.

Fundus photograph of the same eye taken with a red filter demonstrates the refractile nature of the choroidal osteoma.

Late-phase angiogram of the same patient reveals mild staining of the choroidal osteoma. There is no evidence of choroidal neovascularization.

B-scan ultrasonogram of a choroidal osteoma shows a highly reflective, plaque-like structure and an acoustically empty region behind the tumor.

Visual loss in patients with choroidal osteomas may be related to the development of a choroidal neovascular membrane. Note the subretinal hemorrhage in this patient with a large choroidal osteoma.

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is a benign condition that has been mistaken for melanoma and can be confused with a similar abnormality that is associated with familial colon cancer.

Symptoms

Patients with CHRPE are asymptomatic.

Clinical Features

Congenital hypertrophy of the retinal pigment epithelium is a solitary, flat, circumscribed, pigmented lesion that is usually found in the fundus midperiphery. It is often surrounded by a depigmented halo, and it may contain depigmented “lacunae” within the body of the lesion. Congenital hypertrophy of the retinal pigment epithelium (RPE) can become depigmented in older individuals.

By indirect ophthalmoscopy, the lesion may appear to be elevated, but with careful slit lamp biomicroscopy, the lesion is seen to be flat. These lesions are not true tumors and do not grow or produce subretinal fluid.

Lesions similar to CHRPE can be found in clustered groups in a sectorial distribution that resembles “bear tracks.”

Ancillary Testing

Ultrasonography will confirm that the lesion is flat. Fluorescein angiography will show a blocking defect in pigmented areas and a transmission defect in depigmented portions. No intrinsic vessels or dye flush are seen, as with a true tumor.

Pathology/Pathogenesis

Congenital hypertrophy of the RPE is composed of elongated RPE cells that have unusually dense cytoplasmic pigmentation.

Treatment/Prognosis

No treatment is required and the visual prognosis is excellent. Although it is extremely rare, malignant degeneration of CHRPE into an adenocarcinoma has been described; therefore, CHRPE lesions must be followed up regularly.

Systemic Evaluation

Pigmented lesions similar to grouped CHRPE can be seen in familial adenomatous polyposis, which is associated with a high risk of colon cancer. Unlike typical CHRPE, these lesions are usually bilateral, multifocal, asymmetrically distributed, and irregularly shaped. If there is any suggestion of this lesion or a strong family history of colon cancer, the patient should be referred for colonoscopy and further evaluation.

Congenital hypertrophy of the retinal pigment epithelium in a young patient. The lesion is darkly pigmented and flat, with well-defined borders. Note the small, depigmented lacunae.

Fluorescein angiogram of a congenital hypertrophy of the retinal pigment epithelium demonstrating a central blocking defect corresponding to the pigmented portion and surrounding transmission defects corresponding to depigmented areas.

Fundus photograph of a solitary congenital hypertrophy of the retinal pigment epithelium (CHRPE) lesion. Note the multiple lacunae that reveal the underlying large choroidal vessels and sclera characteristic of an

older CHRPE lesion.

Fundus photograph demonstrating the “bear track” pattern of relatively uniform lesions grouped in a sectorial fashion.