Figure 15-3 Optic nerve coloboma. A, Fundus photograph of the right eye shows a colobomatous defect in the inferonasal optic nerve (arrow). B, The gliotic, disorganized retina (asterisk) prolapses into the defect, which is lined by excavated sclera. The normal retina, retinal pigment epithelium, and choroid terminate at the edge of the colobomatous defect (arrows).

(Courtesy of Tatyana Milman, MD.)

Inflammations

Infectious

Infections of the optic nerve may be secondary to bacterial or fungal infections of adjacent anatomical structures, such as the eye, brain, or sinuses, or they may occur as part of a systemic infection, particularly in an immunosuppressed patient. Fungal infections include mucormycosis, cryptococcosis, and coccidiomycosis. Mucormycosis generally results from contiguous sinus infection. Cryptococcosis results from direct extension of the infection from the CNS and often produces multiple foci of necrosis with little inflammatory reaction (Fig 15-4). Coccidiomycosis produces necrotizing granulomas.

Figure 15-4 Cryptococcosis of the optic nerve in an immunocompromised patient. The dura is infiltrated by cryptococcal organisms (arrows). This yeast has a mucopolysaccharide capsule, highlighted with mucicarmine stain. No inflammatory

infiltrate is observed. (Courtesy of Tatyana Milman, MD.)

Viral infections of the optic nerve are usually associated with other CNS lesions. Multiple sclerosis and acute disseminated encephalomyelitis are immune-mediated demyelinating diseases with multifactorial etiologies, including infectious causes. The damaged myelin is removed by macrophages (Fig 15-5). Astrocytic proliferation ultimately produces a glial scar, known as a plaque.

Noninfectious

Noninfectious inflammatory disorders of the optic nerve include giant cell arteritis and sarcoidosis. Giant cell arteritis can produce granulomatous inflammation in the blood vessel wall and occlusion of the posterior ciliary vessels with liquefactive necrosis of the optic nerve. Superficial temporal artery biopsy is the gold standard for histologic diagnosis of giant cell arteritis (Fig 15-6). The involvement of the vessel wall in giant cell arteritis can be patchy (skip lesions). Obtaining a biopsy specimen of adequate length (approximately 2 cm) and performing a careful histologic examination of the specimen can increase the diagnostic yield.

Figure 15-5 Multiple sclerosis, optic nerve. A, Luxol fast blue stain, counterstained with H&E. The blue-staining area indicates normal myelin. Note the absence of myelin in the lower left corner of the optic nerve (asterisk), corresponding to a focal lesion. B, Higher magnification. The blue material (myelin) is engulfed by macrophages.

Figure 15-6 Giant cell arteritis, superficial temporal artery. A, Vascular lumen (arrow) is narrowed by concentric intimal hyperplasia. Prominent transmural inflammatory infiltrate with numerous multinucleated giant cells (arrowheads) is observed. B, Elastic stain highlights the diffuse loss of the internal elastic lamina. A short segment of remaining internal elastic lamina is marked with an arrow. Giant cells (arrowheads) are noted at the level of the internal elastic lamina. I = intima, M = media, A =

adventitia. (Courtesy of Tatyana Milman, MD.)