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

with corticosteroids or interferon (Teske et al. 1994;

Lasjaunias 1997; Achauer and Vander Kam 1989; Bilaniuk 1999).

6.2.2.2

Cavernous Hemangioma

The term cavernous hemangioma is still being controversially discussed, as there is no cellular proliferation but slow enlargement over a period of time (Bilaniuk 1999). Cavernous hemangiomas consist of large ectatic (cavernous) spaces lined by flattened endothelial cells and surrounded by a capsule of fibrous tissue (Jakobiec et al. 1974; Garner 1988). They are thought to arise from pre-existent vascular malformations, the vessels of which are initially collapsed, but become patent and dilated with time due to alterations in arterial or venous pressure changes (Hood 1970; Bilaniuk 1999). Cavernous hemangiomas do not have a prominent arterial supply or show infiltrative expansion, in contrast to capillary hemangiomas of childhood (Atlas and Galetta 1996), an entirely

different lesion. Cavernous hemangiomas are isolated from the orbital vascular system and thus from the systemic circulation (Harris and Jakobiec 1979).

Cavernous hemangioma of the adult type occurs predominantly in the 4th and 5th decade of life and represents an orbital lesion, consisting of large (cavernous) spaces surrounded by a capsule (Hood 1970; Garner 1988). They account for 5%–7% of all orbital tumors and occur predominantly in women.The leading clinical symptom is a slowly progressing, painless, axial exophthalmos (Figs. 6.48, 6.49), occasionally with a mild visual deficit or visual obscurations due to optic nerve compression or extension by stretching (Fig. 6.49). Some 25% of patients have choroidal folds or papilledema. Single and unilateral, multiple tumors may occasionally be observed and are primarily located in the intraconal space. In rare cases, they may be found in the extraconal space (Fig. 6.162) or in the lacrimal gland or even intraosseously (Ruchman and Flanagan 1983; Dyer and Atkinson 1985; Shields et al. 1987a; Ohbayashi et al. 1988; Leatherbarrow et al. 1989; McNab and Wright 1989;

Orcutt et al. 1991; Sullivan et al. 1992a; D’Hermies et al. 1993; Guenalp and Guenduez 1995; Atlas and Galetta 1996; Sweet et al. 1997). Histologically, this tumor has a thin capsule and consists of large vascular channels that are outlined by endothelium.Venous thrombosis is common due to the stagnant circulation, while lymph follicles and inflammatory signs are rare (Figs. 6.48, 5.50).

On imaging, cavernomas demonstrate characteristic features, presenting as a sharply outlined tumor

with medium reflectivity on ultrasound A-scan. On B-scan, the tumor is seen as a round to oval lesion with a smooth surface and regular internal structure (Coleman et al. 1972; Bellone et al. 1974; Bettelheim and Till 1975; Ossoinig et al. 1975; Byrne and

Glaser 1983; Cappaert et al. 1983). The major task of CT, and in particular of MRI, apart from showing the characteristic morphology of a well-defined,round or oval, mainly intraconal (occasionally extraconal) mass that usually, but not always (Fig. 6.50), spares the

orbital apex, consists of the accurate anatomic delineation and definition of the relationship of the mass to the optic nerve and muscle cone (Figs. 6.48, 6.49, 6.51, 6.52). Calcifications correspond to phleboliths, which may be regarded as a pathognomonic sign. Although no deformation of the globe may be seen even in the presence of large tumors, because of the soft consistency of these masses,in the case of rather large lesions a slight expansion of the bony orbit may be apparent (Fig. 6.49) (Jacobs and Kinkel 1976; Gyldenstedt et al. 1977; Davis et al. 1980; Wende et al. 1977; Savoiardo et al. 1983; Sood et al. 1992; Weber 1992;

Atlas and Galetta 1996). Compared with the MRI presentation of orbital fat and muscles, cavernous hemangiomas normally give an isoto hypointense signal in T1-weighted images (Figs. 6.48, 6.51), and some hyperintense areas may be visible in the presence of thrombosis. While contrast enhancement is generally extensive, early images are characterized by an inhomogeneous, heterogeneous signal because of internal septations. In late images, lesion enhancement is homogeneous (Mafee et al. 1987b; Bilaniuk 1999). On T2-weighted images, the lesions exhibit a hyperintense, mostly homogeneous, at times irregular signal.

The most important differential diagnosis is an orbital varix, which may also demonstrate a well-delineated mass, but should be considered if intralesional flow or intermittent exophthalmos is seen on Valsalva maneuver.

The differential diagnosis should further include hemangiopericytoma (Fig.6.92),fibrous histiocytoma, and neurinoma (Fig. 6.40) (Tan et al. 1987; Atlas et al. 1988; Weber 1992; Bilaniuk and Rappoport

1994; Mukherji et al.1994; Zhu et al.1995; Atlas and Galetta 1996; Thorn et al. 1999).

The treatment of choice is periodic observation in cases where no symptoms are present and the tumor was detected incidentally (Fig. 6.53), while complete surgical removal through an anterior medial, lateral orbitotomy, or a transconjunctival approach is indicated when the patient is symptomatic,or the lesion is growing. Shrinkage of the tumor by selective coagulation or aspiration may facilitate removal. The visual prognosis is excellent in most cases; malignant transformation or local recurrence has not been demonstrated.

6.2.2.3

Venous Lymphatic Malformation (Lymphangioma)

The term lymphangioma, which has been used until very recently,should be replaced by venous lymphatic malformation, as it describes a vascular anomaly (Bilaniuk 1999). Occurring in the head and neck, predominantly in children and young adults, this vas-

cular malformation of unknown origin is considered to represent a vascular anomaly with abortive vessels, which spread among normal structures (Harris et al. 1990; Bilaniuk 1999). Venous lymphatic malformation presents as an unencapsulated mass that consists primarily of thin-walled, endothelial-lined, bloodless, vascular and lymph channels, containing numerous cystic spaces of different sizes. They may clinically resemble capillary hemangiomas with the difference of diffuse growth in the absence of spontaneous regression (Graeb et al. 1990; De Potter et al. 1995; Kaufman et al. 1998). The tendency towards spontaneous hemorrhage results in the sudden onset of proptosis combined with periorbital swelling and reduced eye motility, at times leading to optic nerve compression (Katz et al. 1998; Carmody 2000).

On imaging, venous lymphatic malformation presents primarily as an extraconal, although in some instancesintraconal,infiltrative,multilobularmasswith indistinct borders and poor encapsulation (Figs. 6.54, 6.55, 6.165).Since venous lymphatic malformations are slowly growing lesions, an asymmetric enlargement of the orbit may be seen in young individuals (Fig. 6.54). Calcification may be present on CT (Fig. 6.55), while MRI shows an isointense (relative to the brain) mass in T1-weighted series,but a hyperintense signal in proton density or T2-weighted images that corresponds to the presence of a large number of fluid channels. As thrombosis and hemorrhages are known to occur, MRI may show an inhomogeneous signal (Kazim et al. 1992), giving rise to its description as a “chocolate-

cyst”, as well as causing difficulties in its differentiation from a cavernous hemangioma on both imaging and histology.Apart from morphologic characteristics, which in some cases include a bony expansion (Katz et al. 1998), the most important differential diagnostic criterion from idiopathic orbital inflammation and/or hemangiomas is the absence of contrast enhancement (Fig. 6.55) (Kaufman et al. 1998).

6.2.2.4

Orbital Venous Anomaly (syn. “orbital varix”)

The classical definition of a primary orbital varix is that of a venous malformation with abnormal uniand bilateral dilation of one or more orbital veins. Symptoms consist of variable proptosis,associated with an increase in systemic venous pressure (Lloyd et al. 1971; Rootman and Graeb 1988). However, the nomenclature of orbital varix is discussed controversially: Wright et al. (1997) postulate the same underlying abnormality as in venous lymphatic malformations (see Sect. 6.2.2.3) and propose the term “orbital venous anomaly”. As orbital veins do not have valves, systemic venous pressure changes occur during coughing, forced expiration, and

bending forward, and the Valsalva maneuver may cause intermittent proptosis (Cohen et al.1995).Hemorrhage or thrombosis may lead to acute,painful exophthalmos, sometimes with decreased orbital motility (De Potter et al. 1995; Bilaniuk 1999).

On CT, an intraconal, well-defined, elongated mass is seen, generally in the course of the superior ophthalmic vein, which is sometimes marked by calcification, corresponding to small phleboliths. In cases of a primarily occult lesion,Valsalva maneuver or a prone position may be helpful in demonstrating the lesion, due to an increase in orbital pressure (Shields et al. 1984a; De Potter et al. 1995, Bilaniuk 1999). The dilated veins show highly intensive homogeneous contrast enhancement (Fig. 6.56).

In MRI studies, the morphology of orbital varices manifests as a triangular configuration tapering toward the apex and the convex anterior margin (Fig. 6.58). After gadolinium administration, the optimum delineation of signal enhancement in orbital varices is achieved in fat-suppressed series (Fig. 6.57c–e). Gradient-echo sequences may be used to evaluate the blood flow and to perform the Valsalva maneuver (De Potter et al. 1995).