Primary Orbital Lesions

Cystic Lesions

Epithelial and Dermoid Cysts The most common developmental cysts occurring in the orbital and periorbital region and having a predilection for the superotemporal quadrant, are the epithelial and dermoid cysts. Dermoid cysts contain one or more epidermal appendages such as hair follicles, sweat glands, and sebaceous glands; epithelial cysts contain only stratified squamous cell epithelium. Echographi-cally, epithelial and dermoid cysts appear on B scans as smoothly rounded, echolucent lesions with good sound transmission (Figure 8.2A,B). However, some dermoid cysts show low internal amplitude echoes depending on the number of hair shafts and other appendages within the lesion, which invariably cause partial sound attenuation. On A scan, epithelial cysts are low reflective. Dermoid cysts are medium to low reflective with occasional high reflective spikes that indicate the presence of certain coarse structures such as fine hairs or cartilaginous remnants.4,5

Congenital Cystic Eye Congenital cystic lesions contain protrusions through defects present in the walls of microphthalmic eyes. A congenital cystic eye results from failure in the invagination of the primary optic vesicle and lack of differentiation into its adult components. Echographi-cally, the cystic portion shows typical roundish, echolucent B-scan characteristics with very low internal reflectivity on A scan. The microphthalmic globe, on the other hand, is highly dense on B scan with marked shadowing. A-scan echography shows a high reflective structure (typical of condensed tissue structures) with marked sound attenuation almost consistent with calcific structures.

Hematocele

A hematocele is a cystic lesion (Figure 8.2C,D) that results from spontaneous accumulation of blood. Invariably it occurs without preexisting orbital vascular disease.

Vascular Lesions

Infantile Hemangioma A benign vascular tumor (Figure 8.3), infantile hem-angioma usually appears during the first few months of life. The majority of these lesions enlarge in size within the first 2 years and in approximately 70% of the cases undergo spontaneous involution by the age of 7 years. The tumor is generally unilateral (although bilaterality has been reported),6 and it occurs most commonly in the superior nasal quadrant in otherwise healthy children.

Cavernous Hemangioma The most common primary benign orbital tumor of adults (Figure 8.4A-C), cavernous hemangioma usu

FIGURE 8.1. Transocular and paraocular display of normal orbit. A-scan transocular examination of a normal orbit (A, bottom) reveals the following echospikes from left to right: the initial spike (I), which has no clinical significance and represents echoes generated at the tip of the probe (dead zone of the ultrasound probe); the baseline, which is a horizontal line and represents the vitreous cavity (V); the ocular wall spikes (W), which are high reflective echospikes; and the orbital spikes (O), which are multiple high reflective echo spikes ( — 100%) with marked attenuation because of the coarse, dense structures within the orbit. (B) B-scan transocular examination of a normal orbit reveals the following areas from left to

FIGURE 8.1. Transocular and paraocular display of normal orbit. A-scan transocular examination of a normal orbit (A, bottom) reveals the following echospikes from left to right: the initial spike (I), which has no clinical significance and represents echoes generated at the tip of the probe (dead zone of the ultrasound probe); the baseline, which is a horizontal line and represents the vitreous cavity (V); the ocular wall spikes (W), which are high reflective echospikes; and the orbital spikes (O), which are multiple high reflective echo spikes ( — 100%) with marked attenuation because of the coarse, dense structures within the orbit. (B) B-scan transocular examination of a normal orbit reveals the following areas from left to right: an echogenic area (initial line, I), which has no clinical significance and represents echoes at the tip of the probe (dead zone of the ultrasound probe); a clear or echolucent area representing the vitreous cavity (V); and an echogenic area that represents the posterior ocular wall and the orbital tissues (O) behind it. This normal retrobulbar echo pattern is derived from the orbital fat globules, which are triangular; the pattern is indented by a V-shaped, echolu-cent area that represents the optic nerve (ON). The display in paraocular examination (A, top) is similar to that of transocular examination, except for the presence of the cystic structure of the globe. However, the echographic criteria are comparable.

ally appears in the third to fifth decades of life. The tumor is characteristically unilateral and solitary, although multifocal lesions have been reported.7,8 It is most commonly found within the muscle cone, re sulting in slowly progressive proptosis of the globe. On gross examination, cavernous hemangiomas are well-encapsulated, round to ovoid masses with violet hue reflecting the stagnation of poorly oxygenated

FIGURE 8.2. Cystic lesions (A,B) dermoid cyst and (C,D) hematocele. (A) Clinical photograph of a child with right anterior, medial orbital mass. (B) Transocular A scan shows an anterior low reflective lesion (L) shown within smooth high reflective echo spikes that delineate the anterior (a) and the posterior (p) wall of the cystic structure. V, vitreous cavity; W, ocular wall spike; O, orbital tissue spikes. (C) Axial CT scan shows well-delineated round mass (M) in the right orbit. (D) B scan (top) displays a round echolucent orbital lesion (L). A scan (bottom) shows low reflectivity of the lesion (L) with high posterior surface spike (P) from the cyst wall. Occasionally, there are moderately high reflective, dispersed spikes representing lines of clotted blood. I, initial spike; V, vitreous cavity; S, sclera or ocular wall; O, orbital tissue.

Dumbbell Dermoid

FIGURE 8.3. Infantile hemangioma. (A) Clinical photograph of a child with right lower lid hemangioma. (B) B-scan echogram (left) displays an irregular echogenic lesion (L) with variable degrees of sound attenuation. A-scan (right) shows areas of moderate to high reflectivity representative of the cavernous spaces. The capillary portions of the lesion are typically low reflective with intense, diffuse vascularity (dynamic echography). Color Doppler imaging provides an overview of the significant blood flow representative of an active arterial blood supply.5 Histopathology shows (C) proliferation of endothelial cells with numerous small capillaries and (D) areas of cavernous spaces. The intermixing of capillaries and lobulated structures provides the heterogenic components of these lesions.

blood within the tumor. Microscopically, the tumor consists of large, dilated venous spaces lined by thin, flattened endothelial cells, along with pericytes and smooth muscle cells that are separated by irregular fibrous connective tissue septae.

Lymphangioma Lymphangioma is a benign vascular tumor diagnosed in early childhood (Figure 8.4D-F). Unlike infantile hemangioma, lymphangioma enlarges progressively during the growing years. The lymphangioma is non-

FIGURE 8.4. Vascular lesions: (A-C) cavernous hemangioma and (D-F) lymphangioma. (A) Axial CT scan shows well-delineated intraconal mass (M) in the left orbit. (B) B scan displays a well-defined round to ovoid echogenic lesion (L). (C) Ascan reveals multiple, regular, highly reflective echo spikes with the descending edges reaching a medium reflectivity indicating the presence of blood within the venous spaces and the abundant connective tissue septae.9 Sound attenuation is moderate (angle k = 45°). Color Doppler imaging shows little or no evidence of blood flow attributable to the stagnant blood within the

FIGURE 8.4. Vascular lesions: (A-C) cavernous hemangioma and (D-F) lymphangioma. (A) Axial CT scan shows well-delineated intraconal mass (M) in the left orbit. (B) B scan displays a well-defined round to ovoid echogenic lesion (L). (C) Ascan reveals multiple, regular, highly reflective echo spikes with the descending edges reaching a medium reflectivity indicating the presence of blood within the venous spaces and the abundant connective tissue septae.9 Sound attenuation is moderate (angle k = 45°). Color Doppler imaging shows little or no evidence of blood flow attributable to the stagnant blood within the capsulated, often diffuse, with the capability of infiltrating normal tissues. The tumor occurs most commonly in the extraconal space. Spontaneous bleeding within the lesion is a frequent complication. Microscopically, lymphangiomas are formed by endothe-lium-lined, lymph-filled vascular channels separated by loose connective tissue septae that are high reflective. The latter contain fine blood vessels that are responsible for the spontaneous bleeding. Unlike cavernous hemangiomas, pericytes and smooth muscle cells are not present.

vascular spaces.10 (D) Axial CT scan shows an irregular mass (M) in the right orbit. (E) B scan displays an irregular, large lesion (L) with multiple, dilated lymph-filled spaces (arrows).2'11 (F) A scan reveals a regular, heterogeneous pattern with highly reflective echo spikes separated by low reflective, dilated lymphatic spaces. In contrast to cavernous hemangiomas, the presence of clear fluid instead of blood in the wider intracavernous spaces of lymphangiomas provides ample time for the ultrasound beam to reach lower reflective levels (arrows).5 Sound attenuation is moderately low (angle k <30°).

Hemangiopericytoma Hemangiopericytoma is a vascular tumor originating from the pericytes of blood vessels; consequently, it may develop wherever capillaries are present (Figure 8.5).12 Orbital hemangiopericytomas are rare, slow-growing, unilateral tumors with a predilection to the superior orbit. They occur at any age, although the majority appear in adulthood. Microscopically, the tumor consists of spindle-shaped cells packed around thin-walled blood vessels that are lined by endothe-lial cells. The tumor is classified as sinusoidal, solid, or mixed depending on the degree of vascularity between the tumor cells.13 Cystic changes within the tumor may develop secondary to zones of necrosis.

Orbital Varices Primary orbital varices (Figure 8.6A,B) are congenital venous malformations that usually become symptomatic in the second to fourth decade of life. The patient presents with a history of intermittent, positional proptosis. Microscopically, an orbital varix

FIGURE 8.5. Hemangiopericytoma. (A) B-scan echogram displays a well-defined round to oval lesion (L).13-14 The internal structure of the tumor can be irregular, showing solid and cystic components depending on its histopathology. (B) On A scan, the internal reflectivity of the tumor ranges from low (as illustrated) to medium with the latter representing tumor of a mixed nature.14 I, initial spike; V, vitreous cavity; a, anterior and P, posterior surface spikes of the lesion (L); S, sclera. Color Doppler imaging reveals highvelocity blood flow.

FIGURE 8.5. Hemangiopericytoma. (A) B-scan echogram displays a well-defined round to oval lesion (L).13-14 The internal structure of the tumor can be irregular, showing solid and cystic components depending on its histopathology. (B) On A scan, the internal reflectivity of the tumor ranges from low (as illustrated) to medium with the latter representing tumor of a mixed nature.14 I, initial spike; V, vitreous cavity; a, anterior and P, posterior surface spikes of the lesion (L); S, sclera. Color Doppler imaging reveals highvelocity blood flow.

represents an enlarged, dilated vein. The lesion is characterized by a stagnant blood flow that may result in thrombus formation.

Fast-Draining Carotid Cavernous Fistula In fast-draining carotid cavernous fistula, there is a direct communication between the internal carotid artery and the cavernous sinus. This results in dilation of the superior ophthalmic vein (Figure 8.6C,D) with arterialization of blood flow. The patient usually has a history of head trauma and presents with pulsating exophthalmos, a bruit over the globe, dilated and tortuous episcleral vessels, and restriction of motility.

Peripheral Nerve Lesions

Neurofibroma

A benign peripheral nerve tumor, neurofibroma is characterized histopathologically by the proliferation of Schwann cells, peripheral nerve axons, endoneural fibroblasts, and perineural cells. Echographically, neurofibromas are diffuse, irregular lesions with dense internal vascularity that closely resemble infantile hemangiomas. However, the clinical appearance is quite different and is more periorbital with less bluish discoloration.

Schwannoma (Neurilemoma) Schwannoma is a benign peripheral nerve tumor characterized by pure proliferation of Schwann cells. It usually becomes apparent in young to middle-aged adults and is found in 1.5% of patients with neurofibromatosis type 1. The patient generally presents with painless progressive proptosis with downward displacement of the globe, since schwannomas arise more commonly from the supraorbital and supra-trochlear nerves. Histologically, schwannomas show a mixture of two patterns.19 The Antoni type A (dense and cellular pattern) and the Antoni type B (loose, ede-matous pattern forming cystic spaces). Echographi-cally, on B scan, schwannoma appears as a well-defined, roundish, internally echolucent lesion.20 On A scan, the internal structure is quite regular with moderate to low internal reflectivity with the latter representing the Antoni type B areas.

Pseudotumor

An idiopathic orbital inflammatory disorder, pseudotumor occurs mostly in the third to fifth decades of life. The inflammation can be diffuse or localized resulting in periscleritis, sclerotenonitis, tendonitis, myositis, dacryoadenitis, or perioptic neuritis. The patient presents with a sudden onset of unilateral eye pain, redness, chemosis, proptosis, and diplopia.21 Some cases may present with severe chronic inflammation that eventually leads to progressive fibrosis of orbital tissues and results in a frozen globe. Micro-

chapter 8: ultrasonography in orbital differential diagnosis

FIGURE 8.6. Vascular lesions: (A,B) orbital varices and (C,D) fast-draining carotid cavernous fistula. (A). Paraocular A scan shows low internal reflectivity with expansion of the lesion during Valsalva maneuver15 (arrow). (B) On B scan, orbital varices are linear, channeled lesions with echolucent internal structure.5 Sound attenuation is minimal. Color Doppler imaging shows nonpulsatile blood flow with apparent change in dimensions during respiration.16 (C) B scan shows a large, dilated superior ophthalmic vein (B1, arrow) which is typically meandering on sagittal topography.5-17 With dynamic echography, the size of the venous structure changes with the arterial pulsations from a near collapsed size (B3) to a widely dilated channel (B1). (D) A scan shows blurred, low reflective spikes from fast flowing blood (arrow). Sound attenuation is minimal, and color doppler imaging shows a pulsatile, arterial-type blood flow pattern in the superior ophthalmic vein.18

chapter 8: ultrasonography in orbital differential diagnosis

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