See BCSC Section 7, Oculofacial Plastic and Orbital Surgery, for additional discussion of orbital infectious diseases, and Section 8, External Disease and Cornea, for general discussion of microbial and parasitic infections.
Bacterial infections of the orbit
Bacterial infection of the orbit (orbital cellulitis) can occur through direct inoculation (trauma, surgery), spread from infection of adjacent structures (sinusitis), spread from a distant focus (bacteremia), or opportunistic infection (necrotizing fasciitis, mucormycosis). The most common cause of orbital cellulitis is paranasal sinus infection. Infection may be caused by a variety of organisms, including Haemophilus influenzae, Streptococcus, Staphylococcus, Clostridium, Bacteroides, Klebsiella, and Proteus species. The organism most commonly involved differs with age of the patient. Histologically, acute inflammation, necrosis, and abscess formation may be present. Tuberculosis, which rarely involves the orbit, produces a necrotizing granulomatous reaction.
Fungal and parasitic infections of the orbit
Fungal infections of the orbit generally produce severe, insidious orbital inflammation (Fig 14-6). Rhinocerebral or rhino-orbito-cerebral mucormycosis (zygomycosis) usually occurs in patients with poorly controlled diabetes mellitus (especially those with ketoacidosis), solid malignant neoplasms, or extensive burns; in patients undergoing treatment with corticosteroid agents; or in patients with severe neutropenia. Typically, mucormycosis represents spread from an adjacent sinus infection. The specific fungal genus involved is frequently Mucor or Rhizopus. Histologically, inflammation (acute and chronic) is present in a background of necrosis and is often granulomatous. Broad, nonseptate hyphae may be identified with hematoxylin-eosin (see Fig 14-6C), periodic acid–Schiff (PAS), and Gomori methenamine silver (GMS) stains. These fungi can invade blood vessel walls and cause a thrombotic vasculitis resulting in ischemic necrosis. The organisms have the potential for hematogenous spread to the central nervous system (CNS), resulting in stroke and death. Diagnosis is made by biopsy, often of necrotic-appearing tissues (eschar) in the nasopharynx.
Figure 14-5 Immunoglobulin G4–related disease (IgG4-RD). A, CT image from a 67-year-old woman who presented with a 3-year history of an enlarging painless mass of the right lacrimal gland fossa, which was identified on CT as a homogeneously enhancing, circumscribed mass diffusely involving the right lacrimal gland (arrow).B–D, Photomicrographs show extensive collagenous fibrosis, lymphoid follicular hyperplasia, and markedly increased plasma cells. E, Immunohistochemistry reveals frequent IgG4 plasma cells, accounting for 40%–50% of total IgG-positive plasma cells. F, A different area of the lymphoid infiltrate stained for IgG4. A subsequent serum test showed an elevated serum IgG4 level. A diagnosis of IgG4-RD was made.
(Courtesy of Kirtee Raparia, MD.)
Figure 14-6 Fungal infections of the orbit generally produce severe, insidious orbital inflammation. A, Clinical appearance of Aspergillus orbititis, which is similar to the clinical presentation of mucormycosis. B, Microscopic section shows branching fungal hyphae (Aspergillus) on silver stain. C, Mucor hyphae are large and can often be seen on hematoxylin-eosin stain (arrows). The organisms are shown in the wall of the ophthalmic artery.
(Parts A and B courtesy of Hans E. Grossniklaus, MD; part C courtesy of Nasreen A. Syed, MD.)
Aspergillus infection of the orbit from the adjacent sinuses or hematogenous spread from other parts of the body may occur in immunocompromised or otherwise healthy individuals. With its slowly progressive and insidious symptoms, sino-orbital aspergillosis often goes unrecognized, resulting in a sclerosing granulomatous process. Aspergillus is often difficult to culture but may be observed in biopsied tissue as septate hyphae with 45° angle branching (see Fig 14-6A, B). Despite aggressive surgical therapy and adjunct therapy with antifungal agents, if extension into the brain occurs, orbital infections may be fatal.
Allergic fungal sinusitis is a form of noninvasive fungal disease resulting from an immunoglobulin E–mediated hypersensitivity reaction to the organisms in atopic individuals. Several species of fungi can cause the disease, which may extend into the orbit and intracranially in some cases.
Parasitic infections of the orbit are rare, especially in developed countries. They may be caused by Echinococcus species (orbital hydatid cyst), Taenia solium (cysticercosis), and Loa loa (ocular filariasis [loiasis]). These infectious diseases are seen mostly in patients who come from, or have traveled to, areas where the infections are endemic. Serologic studies for specific parasites may aid diagnosis.
Infections of the lacrimal drainage system
Infections can occur in various parts of the lacrimal drainage system and may be acute or chronic. The most commonly affected areas are the canaliculus, resulting in canaliculitis, and the lacrimal sac, resulting in dacryocystitis. Obstruction or the presence of foreign material (eg, dacryolith, punctal plug) may predispose to infection, but infection can develop in the absence of these factors. Bacteria, fungi, and viruses can all cause infection of the lacrimal drainage system, although the filamentous gram-positive bacterium Actinomyces israelii is the most common causative organism in canaliculitis. This organism may form a bacterial aggregate in the lacrimal drainage system, leading to dacryolith formation with a characteristic yellow color, known as a “sulfur granule.” For more information on infections of the lacrimal drainage system, see BCSC Section 7, Oculofacial Plastic and Orbital Surgery.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.