Ординатура / Офтальмология / Английские материалы / Imaging of Orbital and Visual Pathway Pathology_Muller-Forell_2005

weighted and hyperintense on T2-weighted images (Fig. 6.130). Despite significant fat contents in dermoid cysts with a hyperintense signal both on T1weighted and T2-weighted sequences, definite differentiation from fluid may be impossible. The problem is resolved when diffusion-weighted imaging (DWI) is used,enabling specific definition by signal enhancement (Fig. 6.130) (Guenalp and Guenduez 1996; Kaufmann et al. 1998; Dechambre et al. 1999).

Small dermoids do not require immediate therapy and are usually removed within the 2nd or 3rd year of life. Complete removal without rupturing is required in order to avoid inflammatory reactions or local recurrences. Larger orbital dermoids may cause severe effects, including exophthalmos and recurrent inflammations. These conditions require immediate, complete removal, in the majority of cases by lateral orbitotomy with bone resection.

6.3.4.2 Tumors

As discussed above, lacrimal gland lesions can be divided into epithelial and nonepithelial lesions. The classification of lacrimal gland epithelial tumors is similar to that of salivary gland ones and comprises 40%–50% of all lacrimal masses, one-half of which are benign mixed tumors, while the other half constitute malignant masses (Warner et al. 1996).

6.3.4.2.1

Pleomorphic Adenoma (Benign Mixed Tumor)

The most common benign tumor of the lacrimal gland is the benign mixed or pleomorphic adenoma of the lacrimal gland, which originates mainly, but not exclusively from the inner, orbital lobe (Mafee and Haik 1987; Rose and Wright 1992;

Vangveeravong et al. 1996). Clinical signs include a painless, slow-growing mass in the lateral orbit, persisting for more than 12 months, leading in some cases, particularly in middle-aged patients (about 40–50 years of age; without any gender predilection), to proptosis and limited ocular motility (Rose and Wright 1992; Mafee et al. 1999b). The generally encapsulated tumor is characterized by irregular solid parts with myxoid, chondroid, or mucinous areas. Although benign, these tumors can undergo malignant transformation, primarily in cases where only a biopsy or incomplete excision were performed, both of which are associated with a high rate of recurrence (Stewart et al. 1979; Rose and Wright 1992; Mafee et al. 1999b).

Imaging features represent histologic conditions, and the tumors are defined as well circumscribed, encapsulated, round to oval-shaped masses, which might cause lacrimal fossa deformation. On CT, calcifications may be seen, while on MRI, a heterogeneous signal is identified, especially on T2-weighted images with low to moderate contrast enhancement (Fig. 6.131). Irregularity at the edge of the tumor or infiltration of the adjacent orbital tissue may be seen in malignant transformation (Mafee et al. 1999b).

6.3.4.2.2

Adenoid Cystic Carcinoma

Although an uncommon tumor, adenoid cystic carcinoma is the most frequent malignant tumor of the lacrimal gland, accounting for 29% of all epithelial lacrimal gland tumors (Henderson and Farrow 1980; Warner et al. 1996). In contrast to the older patient population with benign mixed tumors, adenoid cystic carcinoma occurs most frequently in the 4th decade of life, although young adults may also be affected (Tellado et al. 1997; Mafee et al. 1999b). Patients present with a hard mass in the upper lateral orbit, often associated with pain caused by the infiltrative perineural growth. Different long-term prognoses for patients suffering from adenoid cystic carcinoma have been reported, ranging from only 5 years in 40% of patients (Font et al. 1998) to an estimated survival rate of 15 years in 58% of patients (Tellado et al. 1997). Histologically, these tumors are characterized by the absence of a mesenchymal matrix, and can be divided into different histologic types according to the predominant cell type. The cell types include tubular, sclerosing, comedo carcinoma, basaloid, or cribriform patterns, the last-mentioned being composed of benign-appearing sheets of basaloid epithelial cells and surrounding spaces of varying shapes and sizes with the characteristic cribriform pattern of Swiss cheese (Tellado et al. 1997; Mafee et al. 1999b).

On CT or MRI, the appearance of a nodular and infiltrative tumor, combined with bone erosion (Fig. 6.132), suggests adenoid cystic carcinoma, especially in the presence of soft-tissue involvement. Although calcification is found in benign mixed tumors, it is more common in malignant lacrimal gland lesions (Mafee et al. 1999b).

6.3.4.2.3

Lymphoma of the Lacrimal Gland

Lymphomatous lesions of the lacrimal gland include a wide spectrum, ranging from reactive lymphoid

hyperplasia, low-grade mucosa-associated lymphoid tissue (MALT) lymphomas, to malignant lymphomas of various types (Jakobiec et al. 1979; Agulnik et al. 2001). Although rare (Galieni et al. 1997), primary lymphomas without systemic involvement appear to be the most common nonepithelial tumor of the lacrimal gland (Rootman et al. 1988). Lymphomas of the lacrimal gland present in older patients as a painless, slowly growing, salmon-colored mass in the upper lateral orbit, in some cases combined with conjunctival redness (25%) or visual impairment (13%) (Polito et al. 1996; Mafee et al. 1999b). As radiotherapy and chemotherapy promise complete remission in most cases, an accurate histological or cytological diagnosis should be achieved by biopsy (Jeffrey et al. 1995; Galieni et al. 1997; Agulnik et al. 2001).

Although imaging of patients with lymphoproliferative disorders is characterized by nonspecific features, making the differential diagnosis with respect to acute or chronic idiopathic orbital inflammation, metastasis, capillary hemangioma, and plexiform neurofibroma difficult, specific features may lead to the diagnosis of lymphoma: Lymphoid tumors frequently have a superior orbital or retrobulbar component, show straight or angulated edges, as they grow along orbital fascial planes and muscles,and a striped profile on infiltrating retrobulbar orbital fat (Yeo et al. 1982). CT and MRI show one or more,lobulated or round,slightly isodense/ isointense masses,molding adjacent structures without causing indentation (Figs. 6.44, 6.133–6.135). In addition,a wedge-shaped enlargement of the lacrimal gland

causing a smooth impression of the orbital walls without bone erosion is apparent,while substantial destruction and invasion of the adjacent tissue,including bones and the brain,is seen in malignant variants (Figs.6.136, 6.137) (Yeo et al. 1982; De Potter et al. 1995; Polito et al.1996; Mafee et al.1999b).Lymphomas are usually bulkier than idiopathic orbital masses; they may mold and drape onto the globe, with more frequent evidence of anterior or posterior extension (Mafee et al. 1999b) and symmetric, bilateral involvement (Fig. 6.138). An important diagnostic criterion on MRI is moderate to marked hyperintensity of the extraocular muscles and the orbital fat on T2-weighted images. On T1-weighted images,lymphomas exhibit hyperintensity in comparison with the extraocular muscles, hypointensity compared with the orbital fat,as well as moderate to marked enhancement in fat-suppressed, gadolinium-enhanced images. These factors make a reliable differentiation from the above-mentioned pathologies difficult (De Potter et al. 1995; Asao et al. 1998).

6.3.4.2.4

Miscellaneous (Amyloid Tumor, Extramedullary Plasmocytoma)

In contrast to diseases due to degeneration and amyloid deposits, focal amyloidosis is a very uncommon disorder that may present either as a mass or with diffuse infiltration.It may involve different orbital structures as, e.g.,orbital fat (Fig.6.82),external muscles (Okamato et al.1998),or the lacrimal gland (Fig.6.138) (Motta et al.

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Orbital Pathology

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Fig. 6.134a,b. An 82-year-old woman with painless proptosis of the left eye persisting for 2 weeks. Diagnosis: non-Hodg- kin lymphoma of the lacrimal gland. Contrast-enhanced CT: a Axial view with slightly enhancing mass of the left lacrimal gland, flattening the circumference of the left globe. c Corresponding coronal view where the extra-axial inferior dislocation of the bulb is more distinct than in a

1983; Levine and Buckman 1986; Conlon et al. 1991; Murdoch et al.1996).Isolated involvement of the lacrimal gland may mimic inflammatory or even tumorous lesions (Mafee et al. 1999b). Clinically presenting with painless proptosis, amyloidoma of the lacrimal gland is associated with an enlarged gland, molding to adjacent orbital structures, and frequently with punctuate calcification (Fig. 6.139), resembling phleboliths, which is best identified with CT (Fig. 6.82) (Massry et al. 1996). With MRI,amyloid deposits show hypointensity on T2weighted images (Fig. 6.82) (Mafee et al. 1999b). With both imaging modalities, they demonstrate virtually no contrast enhancement (Cohen and Lessell 1979;

Okamoto et al. 1998).

As tumors of the lacrimal gland behave in a similar fashion to those of the salivary or parotid gland, extramedullary plasmocytoma may also be seen in the lacrimal gland, sometimes mimicking amyloid deposition (Ustun et al. 2001). A rare entity, belonging to the category of non-Hodgkin lymphoma, they represent up to 4% of all plasma cell tumors. Extramedullary plasmocytoma primarily involves the nasal cavity and the paranasal sinus (Alexiou et al. 1999; Liebross et al. 1999; Galieni et al. 2000), while orbital involvement is extremely rare (Fig. 6.140) (Uceda-Montanes et al. 2000). The tumors most fre-