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

may also be suggestive (Mauriello and Flanagan 1989). The differential diagnosis may be difficult when imaging shows a lack of infiltration, distortion of the shape of the globe, or bony erosion, especially in the tumefactive type of idiopathic orbital inflammation (Flanders et al. 1989).

As mentioned above, idiopathic orbital inflammation may involve all orbital compartments and exhibit different patterns. Typical characteristics include painful, acute to subacute, mostly unilateral proptosis,

combined with imaging findings of diffuse infiltration, swelling, and/or contrast enhancement of several intraorbital tissues (Figs. 6.65–6.67); it further may occur in a localized form in the intraand extraconal compartment.Although usually confined to the orbital soft tissue, idiopathic orbital inflammation with or without mass effect can produce bone destruction and extraorbital extension (De Potter et al. 1995). In diffuse idiopathic orbital inflammation, CT and MRI show an infiltrative process of orbital fat with a

reticular pattern and variable contrast enhancement (Fig. 6.65). On MRI it is best seen on fat-suppressed T1-weighted images, where signal enhancement is marked in the acute form and minimal to moderate in the sclerosing and chronic type of idiopathic orbital inflammation (De Potter et al. 1995) (Fig. 6.64).

The differential diagnosis should comprise scars (Fig. 6.68), and in the presence of bilateral involvement, the possibility of xanthogranulomatous (lipoid) cell infiltration should be considered. In Erdheim-Chester disease (Fig. 6.69), a rare sporadic, systemic, histiocytic disorder of unknown etiology in adults, the patient presents with fibrosing xanthogranulomas, composed of xanthomatous histiocytes, fibrosis, and Touton giant cells. They are mainly found in the bone (Fig. 6.69), but may affect multiple organ systems, as lung involvement and retroperitoneal fibrosis are found (Egan et al. 1999). The histological features of foamy histiocytes may overlap with Langerhans’ cell histiocytosis (see Sect. 6.3.1.4.3, 7.2.1.2.3, Fig. 5.19), but age and negative immunohistochemical staining with CD-1a and S100 should lead to the diagnosis of Erdheim-Ches- ter disease (van der Lee et al. 1999). Corticosteroids might be efficacious, but the clinical course is potentially fatal. Orbital involvement is an uncommon manifestation,with usually bilateral xanthomatous infiltration of the anterior orbital fat, rarely the extraocular muscles and lacrimal gland (Shields et al. 1991; Jakobiec et al. 1993; Valmaggia et al. 1997; Wright et al. 1999). An extremely rare finding is the involvement of the entire orbit (Fig. 6.69), leading to compressive optic neuropathy and consecutive visual and eye movement deficits, but the combination with adjacent bone involvement like the sphenoid and sphenoid sinus may lead to a specific diagnosis.

Myositis is the local presentation of an idiopathic orbital inflammation with preferred involvement of only one external muscle. The combination of painful, acute proptosis with swelling of one affected muscle combined with impaired motility may be regarded as pathognomonic. Imaging demonstrates not only the enlarged muscle, but also inflammation of the tendon, a characteristic sign (Figs. 6.70–6.72). The most important differential diagnosis is that of Graves’ disease, where the enlargement of the external muscle spares the tendon.

Fig. 6.65. A 4-year-old girl with progressing proptosis of the right eye and inflammatory constellation. Diagnosis: diffuse idiopathic orbital inflammation. The contrast-enhanced CT shows enhancement of all structures of the right orbit: the conjunctiva, sclera, rectus muscles, as well as the orbital fat

Fig. 6.66. Axial CT of a 10-year-old girl with painful, progressive exophthalmos of the right eye. Diagnosis: diffuse idiopathic orbital inflammation. Diffuse scleral thickening of the entire circumference, distinct, hazy hyperdensity of the retrobulbar fat, diffuse swelling of the lateral rectus muscle, including the tendinous insertion (arrow), but not affecting adjacent structures. (With permission of Müller-Forell and Lieb 1995b)

a

c

6.2.3.2

Endocrine Orbitopathy (Syn. Graves’ Disease)

Dysthyroid endocrine orbitopathy is the most frequent cause of unior bilateral proptosis in adults. The clinical presentation of slowly progressing proptosis in this genetically determined autoimmune disease of the rectus muscles and the orbital connective tissue may be the first symptom in the course of autoimmune hyperthyroidism (morbus Basedow) or Graves’ disease (Weetman and Hunt 1999; Pappa et al. 2000; Wiersinga and Prummel 2001). Apart from the classic clinical and ophthalmologic signs including conjunctival injection, lid retraction, and disturbance of motility, and endocrinological findings, imaging is indicated for the primary diagnosis as well as for follow-up examinations in the course of the disease. The extraocular muscles are the main targets with T-cell infiltration in the early stage of the disease and increased HLA-DR antigen expression on fibroblasts at all stages, suggesting an early immunosuppressive therapy in order to influence late fibrosis (Pappa et al. 2000). In addition to the extraocular muscles, lymphocyte inflammation, mucopolysaccharide and plasma cell infiltration leading to tissue edema involve all orbital structures (including the

b

Fig. 6.72a–c. A 49-year-old woman with painful proptosis of the left eye, presenting with chemosis. Diagnosis: myositis of the left medial rectus muscle. a Portrait of the patient. CT: b Axial view, demonstrating thickening of the left medial rectus muscle, including the tendon. c Coronal view demonstrating the exclusive involvement of the medial rectus muscle

lacrimal gland). As bilateral involvement is more frequent than unilateral involvement (Char 1990; Kahaly et al. 1996), the preferred and primarily involved structures are the inferior and medial rectus muscles, followed by the superior and lateral orbital muscles (Fig. 6.73).

The most important morphological diagnostic criteria of endocrine orbitopathy include spindleshaped spreading of the rectus muscles (>4 mm) without involvement of the tendon (Peyster and Hoover 1984) (Figs. 6.73, 6.74) and compression of the optic nerve in the orbital apex (“crowded orbital apex syndrome”; Neigel et al. 1988; Nugent et al. 1990) (Figs. 6.75, 6.76). An extended course of the disease may lead to a corresponding impression of the lamina papyracea – the normally parallel configured medial wall of the orbit – similar to spontaneous decompression (Fig. 6.75) (Nowinski and

Flanagan 1986).

Volume measurements demonstrate an additional significant increase in retrobulbar fat (Fig. 6.77), predominantly in men, with a good correlation to the proptosis and duration of the disease (MüllerForell et al. 1999). In more chronic stages, collagen deposition in the affected muscle results in fibrosis, and may be associated with fat accumulation (Fells

et al. 1994), which is best seen on MRI. T1-weighted images show signal enhancement of the fatty degeneration, corresponding to hypointensity after i.v. gadolinium and fat suppression (Fig. 6.74).

In contrast to CT, where density measurements do not provide satisfactory answers to important questions regarding the acuteness of the disease,MRI offers the required additional information. On T2-weighted images, an increase in water content with a corresponding signal enhancement indicates the increased lymphocyte and mucopolysaccharide concentration of the involved inflamed muscle. Measurements of T2 relaxation time, using a T2-weighted multi-echo sequence, show lengthening of the affected muscles compared with the uninvolved ones, thus allowing the differentiation between an acute and chronic course

of the disease (Hosten et al. 1989; Just et al. 1991). A prolongation of the calculated T2 relaxation time is seen in the presence of acute inflammation of the rectus muscle (Figs. 6.73, 6.76). A combination with fat-suppression techniques (STIR) further enables the detection of possible edema in the retrobulbar fat tissue (Hiromatsu et al. 1992; Pauleit et al. 1997). This differentiation is of the greatest interest with regard to the decision as to whether the patient may or may not benefit from immunosuppressive and/or radiation therapy (Utech et al. 1995; Pauleit et al. 1997). In rare cases where the evaluation of the acuity of Graves’ disease is exceedingly difficult, an (expensive) extremely sensitive nuclear medical method is applied. Because in active Graves’ disease activated lymphocytes express the somatostatin receptor

octreotide, the local accumulation of octreotide in the orbital tissue can be demonstrated as a marked somatostatin receptor analogue that accumulates only in orbital tissue of high activity (Krenning et al. 1993; Kahaly et al. 1995) (Fig. 6.78).

In summary, we consider MRI to be the most effective tool in establishing the initial diagnosis of endocrine orbitopathy.Although the anatomic differentiation of orbital structures is similar for both CT

and MRI, we prefer MRI for the primary diagnostic procedures not only because of the absence of invasiveness (radiation burden), but also due to its capability of differentiating between acute inflammatory and chronic stages of the disease.

The increase in orbital volume may lead to compression of the optic nerve in the orbital apex with corresponding venous congestion (the so-called “crowded orbital apex syndrome”; Neigel et al. 1988),