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

6.2.2.5

Thrombosis of Orbital Veins

Orbital vein thrombosis, whether in varicoid veins or secondary to different primary diseases, is characterized by an intravasal mass in the dilated superior ophthalmic vein. Depending on the imaging technique used, a primarily hyperdense, dilated superior ophthalmic vein without enhancement after administration of iodinated contrast is seen on CT (Fig. 6.59). On MRI, the appearance depends on the age of the thrombosis and the paramagnetic hemoglobin properties. The absence of the signal void within a dilated superior ophthalmic vein suggests the diagnosis, which is confirmed by a hypointense signal on T1-weighted and T2-weighted images in the presence of deoxyhemoglobin, both of which increase in the presence of methemoglobin (De Potter et al. 1995).

6.2.2.6

Carotid-Cavernous Fistula (CCF)

The carotid-cavernous fistula represents an arteriovenous shunt of the internal carotid artery in its cavernous compartment, leading to arterialization of the

superior ophthalmic vein. The resulting venous congestion of the orbit causes hypervolemia of the globe and orbit, clinically manifesting as pulsatile exophthalmos (identified on auscultation), combined with dilated episcleral vessels, chemosis, secondary glaucoma, eventually also featuring papilledema, ocular pain, and ophthalmoplegia (Flanagan 1979). The described pathologic mechanisms may lead to vision loss as a result of increased intraorbital pressure.

Color-coded ultrasound can definitively demonstrate reversal of blood flow (Fig. 6.60b). On imaging, proptosis combined with enlargement of extraocular muscles and widening of the superior ophthalmic vein is indicative of CCF. It is seen on CT with contrast enhancement after iodinated contrast medium (Fig. 6.60a), and on MRI due to the signal void of the arterialized flow in the superior ophthalmic vein. Although on both CTand MR-angiography a diagnosis of CCF can be done (Figs. 6.61, 6.62) (De Potter et al. 1995; Coskun et al. 2000), imaging techniques give only insufficient information concerning the flow dynamics in terms of differentiating precise flow characteristics. The etiology of CCF may be traumatic (Fig. 6.61) or spontaneous (Fig. 6.62), with the latter occurring primarily in diabetic older

women (Fig. 6.63). The therapeutic regimen does not depend on the etiology but on the flow characteristics, whether the symptoms are caused by a so-called high-flow or low-flow fistula.

Digital subtraction angiography (DSA) is the examination of choice in defining the CCF type. Pathophysiological classification of CCF into highflow (type A) (Figs. 6.60–6.62) and low-flow (type B) fistula (Fig. 6.63) is crucial in determining the definite therapy (Debrun 1993). In high-flow fistula, interventional neuroradiological procedures with

balloon and/or coil embolization, used to occlude the site of the ICA injury (Figs. 6.61, 6.62), will protect against or even reverse the threat of vision loss. In some cases, therapy for low-flow fistula may be unnecessary, since these frequently close spontaneously (Debrun 1993).

The differential diagnosis of a dilated superior ophthalmic vein should include not only CCF, but also consider cerebral arteriovenous malformation (AVM) with atypical venous drainage (e.g.,AVM of the vein of Galen, type II) (Berenstein and Lasjaunias 1992).

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Fig. 6.60a–d. A 48-year-old woman with slowly progressing, bilateral proptosis associated with bruit. Diagnosis: spontaneous carotid-cavernosus fistula (CCF, type A) of the left ICA. CT: a Axial contrast-enhanced image with bilateral dilation of the superior ophthalmic vein with emphasis to the left, suggesting the presence of free flow in the intercavernous sinus. b Color duplex sonography demonstrating a severely dilated superior ophthalmic vein (red) with reversal of flow direction and arterial pulsatile Doppler spectrum. Assessment of the flow velocity enables the differentiation between a high-flow and low-flow fistula. c DSA of the left ICA (arrowheads) in lateral view: The origin of the arteriovenous fistula (large arrow) of the ICA is identified in the cavernous sinus. As a result of the large shunt volume, not only are the cavernous sinus and the superior ophthalmic vein (star) filled, but also the pterygoid venous plexus, the superior petrosal sinus, and the internal jugular vein (small arrows); however, there is no evidence of filling of the intracranial vessels. d Corresponding anteroposterior (AP) view with identification of the site of the fistula (large arrow), ipsilateral ophthalmic superior vein (large star), superior petrosal sinus (small star), and intercavernous sinus (small arrow). (With permission of Müller-Forell and Lieb 1995b)

6.2.3

Inflammatory Lesions

6.2.3.1

Idiopathic Orbital Disorders (“Orbital Pseudotumor”)

Since the commentary of Rootman (1998), the term orbital pseudotumor, previously used to classify a vast range of diseases of diverse character and etiology, should be discontinued. Since this term has contributed to diagnostic confusion both clinically and pathologically, it should be replaced by a more specific definition regarding the clinical and pathophysiological underlying patterns. Although the diversity of underlying disorders represents the most frequent pathologic processes of the orbit and, in particular, of the globe, and the third most common ophthalmologic disease after Graves’ and lymphoproliferative diseases (Weber et al. 1996a; Zurlo et al. 1999), there are four major clinical processes that may affect any structure of the orbit. These include inflammatory, infiltrative, mass effect, and vascular changes that present with different but specific clinical symptoms. Following consideration of a specific finding on imaging study, the age of the patient, systemic evaluation, testing, and biopsy, the diagnosis can be made in an individual case (Rootman 1998). A biopsy is required upon the detection of a nonspecific, possibly granulomatous, benign orbital inflammation without evidence of specific local or systemic disease to exclude the possibility of other diseases. However, systemic steroid therapy without prior biopsy confirmation may be regarded as a pragmatic therapeutic strategy in the majority of cases. Care should be taken not to misinterpret the rapid improvement as being pathognomonic, since many tumors (especially lymphomas) are characterized by a similar presentation and may only be differentiated by biopsy (Mombaerts et al. 1996).

Inflammatory signs and symptoms consist of painful proptosis, warmth, loss of function including blurred vision, and mass effect (Harnsberger 1990; Casper et al. 1993; Rootman 1998). In an acute or subacute course, symptoms develop in days or weeks, while the chronic form may develop over a period of months, striking either sex at any age (Henderson 1994). Infiltrative changes are characterized by evidence of destruction, entrapment, or both, making the differential diagnosis from neoplasia or chronic infiltrative/inflammatory processes difficult. Mass effect consists of orbital structure displacement without or with signs of involvement of sensory or neu-

romuscular structures, while vascular changes show alterations in the character, size, or structural integrity of the vessels (Rootman 1998).

Histologically, cellular components are extremely variable (Mombaerts et al. 1996), consisting of mature lymphocytes, lymphoid follicles, plasma cells, neutrophil and eosinophil granulocytes, histiocytes, and macrophages (Rootman et al.1988c,1994),while vascular changes consist of capillary proliferation with lymphocytic infiltration (Henderson 1994).

Bilateral involvement is considered to be a manifestation of chronic, progressive, immune-mediated, generalized fibrosis, observed in patients with additional retroperitoneal fibrosis (Ormond disease) or in Erdheim–Chester disease (Fig. 6.69) (Levine et al. 1993; Flanders et al. 1989; Shields et al. 1991; McCarthy et al. 1993; Mombaerts et al. 1996;

Valmaggia et al. 1997; Schaffler et al. 2000; Sheidow et al. 2000). The differential diagnosis of the latter two conditions is not readily achieved based on clinical symptoms and imaging findings, and a biopsy should be carried out.

The classification of idiopathic orbital disease varies, with some authors making a division on the basis of the temporal course into the clinical stages of acute or chronic (Bilaniuk et al. 1990), or according to the specific localization of the inflammatory process (Mafee 1996). We prefer a morphologic classification according to diffuse and local forms (Harnsberger 1990; De Potter et al. 1995; Casper et al. 1993). Though this classification dates from the time of the so-called “orbital pseudotumor”, in our opinion a classification into diffuse or local involvement still remains useful in clinical terms. In diffuse idiopathic orbital inflammation, every orbital structure may be involved to a different degree, whereas in the localized form, only one of the different parts of the orbit, i.e., the globe, fat, or muscles, are affected (see scleritis 6.1.3.1, perineuritis 6.4.2.1).

Although nonspecific,the most frequently observed CT and MRI finding characteristic of idiopathic orbital inflammation is contrast enhancement,due to the high vascularity of the inflammatory process (Figs. 6.64, 6.65, 6.66), infiltration of the fat, proptosis, and an isolated or general, unior bilateral, extraocular muscle enlargement (Flanders et al. 1989). The MRI appearance of hypointensity on T2-weighted images relative to normal muscle signal intensity may differentiate idiopathic orbital inflammation from metastatic tumors or vascular congestion (Atlas and Galetta 1996). In the differential diagnosis from true orbital tumors (e.g., lymphomas), the abrupt, mostly painful clinical onset with blurred vision at an early stage