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Neuroradiology Case of the Week

Case 171

Jerry Lee, MD and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 23-year-old male with syncope and collapse.

Radiological Findings: Noncontrast enhanced head CT demonstrates incidental finding of bilateral small rounded, high-density or calcifications at the optic disc surface. (Fig. 1).

Diagnosis: Optic Nerve Drusen

Discussion:
Intraocular Calcifications
      The pathophysiology of calcium deposition in ocular tissues depends on the specific site. Intraocular calcifications may be metastatic (hypercalcemic states), dystrophic or be associated with degenerative ocular conditions (neoplasia, inflammation, congenital dysplasias, and aging or traumatic degeneration). Calcifications in neoplasms may be a result of tumor necrosis such as retinoblastoma and astrocytic hamartomas as seen in tuberous sclerosis or neurofibromatosis type 1. Congenital vascular lesions as in Sturge-Weber syndrome and Von Hippel-Lindau disease may be a cause of calcification. Chronic posttraumatic degeneration is probably the most common cause of dystrophic intraocular calcification. Other common causes include choroidal osteoma, episcleral choristoma, and optic disc drusen. Scleral calcification may be seen in elderly people at or anterior to the sites of insertion of the horizontal extraocular muscles. The table below lists the major causes of intraocular calcification.

Optic Nerve Drusen
      Optic nerve drusen is a benign, usually bilateral cause of pseudopapilledema and is occasionally inherited as an autosomal dominant condition. Drusen has been reported in 20 to 24 per 1000 patients at autopsy and are bilateral in 73% of cases. Disc drusen or hyaline bodies are spherical, acellular, laminated concretions partially calcified and possibly related to accumulation of axoplasmic derivatives or degenerating retinal nerve fibers. Optic disc drusen are rarely seen in early childhood, however, most drusen are believed to be present at birth. They become more apparent later in life as they enlarge and approach the disc surface becoming opthalmologically visible as hyaline or colloid bodies. When drusen are located well beneath the surface of the disc, they may blur the disc margin and may lead to misdiagnosis of papilledema. CT scans detect drusen only when they become calcified and appear as discrete, rounded, high-density or calcified bodies that are confined to the optic disc surface. Clinically, drusen are usually asymptomatic, however, peripheral field constrictions may be present. There also appears to be an association between drusen of the optic disc and retinal hemorrhages.

References:

1. Som PM, Curtin HD. Head and Neck Imaging, 4th ed. St. Louis, Mosby, 2003: 475-477, 479,498 .