CHAPTER 14
Orbit
Topography
Bony Orbit and Soft Tissues
Seven bones form the boundaries of the orbit (see Figures 1-1 through 1-3 in BCSC Section 7, Orbit, Eyelids, and Lacrimal System). These 7 bones are the frontal, zygomatic, palatine, lacrimal, sphenoid, ethmoid, and maxillary.
The orbital cavity is pear-shaped and has a volume of 30 cc. Structures and tissues occupying the cavity are the globe, lacrimal gland, muscles, tendons, fat, fascia, vessels, nerves, sympathetic ganglia, and cartilaginous trochlea. Inflammatory and neoplastic processes that increase the volume of the orbital contents lead to proptosis (protrusion) of the globe and/or displacement (dystopia) from the horizontal or vertical position. The degree and direction of ocular displacement help to localize the position of the mass.
Figure 14-1 A, Clinical appearance of dermoid cyst of the right orbit. Note the typical superotemporal location. B, Lowpower photomicrograph discloses a cyst lined by keratinized stratified squamous epithelium. C, The wall of the cyst contains
sebaceous glands (arrows) and adnexal structures. (Part A courtesy of Sander Dubovy, MD; parts B and C courtesy of Hans E. Grossniklaus, MD.)
Figure 14-2 Nonspecific orbital inflammation (NSOI; orbital inflammatory syndrome). Note the skeletal muscle fibers (arrows) surrounded by a dense infiltrate of chronic inflammatory cells. Unlike thyroid eye disease, in which the tendons of the muscles typically are spared, this condition can affect any orbital structure, including the muscle tendons.
Figure 14-3 Nonspecific orbital inflammation. A, Note the mixture of inflammatory cells and the bundle of collagen (asterisk) running through the orbital fat. B, Diffuse fibrosis dominates the histologic picture of this fibrosing orbititis, considered by some authorities to represent a later stage of the condition illustrated in part A.
Figure 14-4 Thyroid eye disease. A, Clinical appearance demonstrating asymmetric proptosis and eyelid retraction, most prominent on the right side. B, CT scan (axial view) showing fusiform enlargement of the extraocular muscles (asterisks). C, The muscle bundles of the extraocular muscle are separated by fluid, accompanied by an infiltrate of mononuclear
inflammatory cells. (Parts A and B courtesy of Sander Dubovy, MD.)
Figure 14-5 Aspergillus infections of the orbit generally produce severe, insidious orbital inflammation. A, Clinical appearance. B, Microscopic section demonstrates the branching fungal hyphae on silver stains.
MD.)
Figure 14-6 Pleomorphic adenoma (benign mixed tumor) of the lacrimal gland. A, Clinical appearance. A superotemporal orbital mass is present, causing proptosis and downward displacement of the left globe. B, CT scan (coronal view) demonstrating left orbit tumor. C, Low power shows the circumscribed nature of this pleomorphic adenoma. D, Note both the epithelial (arrows) and the mesenchymal (asterisk) elements. E, Well-differentiated glandular structures (epithelial component)
with lumina (asterisks). (Parts A and B courtesy of Sander Dubovy, MD; parts C–E courtesy of Hans E. Grossniklaus, MD.)
Figure 14-7 Adenoid cystic carcinoma of the lacrimal gland. Note the characteristic cribriform (Swiss cheese) pattern of
tumor cells. (Courtesy of Ben J. Glasgow, MD.)
Figure 14-8 Low-grade B-cell lymphoma of the orbit. A, Low-power photomicrograph shows a dense lymphoid infiltrate with a vague follicular arrangement. Note poorly defined follicles or germinal centers (arrows). B, Higher magnification shows small lymphocytes with mild nuclear membrane abnormalities, plasma cells, and atypical lymphocytes with cytoplasmic clearing (monocytoid B cells, arrow). (Courtesy of Ben J. Glasgow, MD.)
Figure 14-9 Lymphangioma. A, Clinical appearance. A young boy with an inferior orbital lesion extending anteriorly and nasally below the left lower eyelid. B, CT scan (axial view) showing a multilobulated mass (white circles) within the left orbit. C, Photomicrograph shows numerous vascular channels and lymphoid follicles (arrow) with a fibrotic stroma. D, Higher magnification demonstrates the lymphocytes and plasma cells within the fibrous walls. (Parts A and B courtesy of Sander Dubovy,
MD; parts C and D courtesy of Ben J. Glasgow, MD.)
Figure 14-10 Cavernous hemangioma. A, CT scan (axial view) showing a well-circumscribed retrobulbar mass (asterisk).
B, Large spaces of blood are separated by thick septa. (Part A courtesy of Sander Dubovy, MD; part B courtesy of Hans E. Grossniklaus, MD.)
Figure 14-11 Fibrous histiocytoma. This photomicrograph illustrates the storiform (matlike or whorly) pattern.
Figure 14-12 Hemangiopericytoma. A, Photomicrograph demonstrates a dense, cellular tumor with a characteristic branching vascular pattern. B, Higher magnification demonstrates closely packed cells with oval to spindle-shaped, vesicular
nuclei. (Courtesy of Ben J. Glasgow, MD.)
Figure 14-13 Rhabdomyosarcoma. A, Child with a large right orbital mass. B, CT scan (axial view) showing a large, poorly
circumscribed orbital tumor (asterisk) and proptosis. C, In this embryonal example, cross-striations (arrow) representing Z- bands of actin-myosin complexes within the cytoplasm of a tumor cell can be identified. D, Poorly cohesive rhabdomyoblasts separated by fibrous septa (arrows) into “alveoli” are low-magnification histologic features of the alveolar variant of rhabdomyosarcoma. This variant may have a less favorable natural history than the more common embryonal
type. (Parts A and B courtesy of Sander Dubovy, MD.)
Figure 14-14 Plexiform neurofibroma. A, Clinical photograph depicting a typical S-shaped deformity of the upper eyelid. B, Note the thickened, tortuous nerves (arrows) with proliferation of endoneural fibroblasts and Schwann cells. (Part A courtesy of
Sander Dubovy, MD.)
Figure 14-15 Neurilemoma (schwannoma). A, The Antoni A pattern. Spindle cells are packed together. B, Palisading of nuclei may form a Verocay body (asterisk). C, The Antoni B pattern consists of a loosely arranged, mucoid stroma and represents degeneration within the tumor.
Figure 14-16 Fibrous dysplasia. Bony trabeculae are C-shaped (arrow), composed of immature woven bone, and surrounded by a fibrous stroma.