Imaging Findings

Among all the small vessel vasculitides listed in the Chapel Hill classification, Wegener granulomatosis is by far the most common in the ENT area (up to 90% of patients) (Jennette and FALk 1997), basically involving three anatomic subsites, namely, sinona-sal cavities and orbit, middle ear and mastoid, and larynx.

Wegener granulomatosis manifestations in the nose and paranasal sinuses are extremely polymorphic; they may consist of mucosal and/or bone changes. Mass-like pseudotumor lesions are reported more commonly in the orbit.

In Wegener granulomatosis, optimal imaging techniques should provide high contrast resolution to accurately depict subtle soft tissue changes observed in the sinonasal area as well in the adjacent deep spaces of the face. For these reasons, though CT enables excellent demonstration of bone changes, MR should be considered as the first line imaging technique when ever Wegener granulomatosis is suspected at clinical examination and laboratory tests.

According to a recent classification (MuhLE et al. 1997), mucosal changes in the early stage of the disease result in rather nonspecific MR findings. Thickening combined with TSE T2 hyperintensity of the epithelial and submucosal layer of the nose and sinus cavities can be observed, reflecting edema and inflammatory cell infiltration in the areas of vasculi-tis. Though sensitive, this MR signal pattern can be nonspecific in up to 37% of patients.

In the late stage of the disease, signal intensity of mucosa and submucosa switches to hypointensity on both TSE T2 and SE T1 sequences, with variable degrees of contrast enhancement (Fig. 6.25). This is mostly due to submucosal accumulation of dense collagen fibers with granuloma formation. In this stage, the specificity of MR significantly increases (up to 100%) (MuhLE et al. 1997).

Evidently, CT discrimination between early and late stage of Wegener granulomatosis is almost impossible as both conditions are displayed as nonspecific mucosal thickenings at times associated with intrasinusal fluid levels (LLOYd et al. 2002).

In advanced stages of the disease, inflammatory infiltrate and granulomatous lesions within small vessel walls lead to obliteration of the lumen and, as a consequence, to avascular necrobiosis. This is the pathologic basis of bone destruction, a hallmark of this disease, reported with different rates of prevalence (8%-75%) (MuhLE et al. 1997; TrimArchi et al. 2001; LLOYd et al. 2002;). The width of this process is also somewhat controversial. Whenever an early diagnosis of Wegener granulomatosis is obtained and proper treatment promptly instituted, this finding is rare (12% of patients) and limited to the nasal septum (TrimArchi et al. 2001). Conversely, in late stages of the disease, a bilateral symmetric destructive pattern, also involving the middle and inferior turbinate, medial maxillary sinus wall, lamina papy-racea, and cribriform plate, is described (LLOYd et al. 2002).

Alternatively, new bone apposition may prevail resulting in sclerotic thickening of bony structures such as sinus walls. Within sclerotic bone, hypodense areas have been described (LLOYd et al. 2002) with fat tissue signal on MR, probably reflecting bone marrow accumulation.

Mass-like pseudotumoral lesions are more commonly described in the orbit (Fig. 6.26), either as a primary involvement or as a secondary spread from contiguous deep spaces of the face, such as the pterygopalatine fossa or masticator space (Fig. 6.27)

Masticator Fossa

Fig. 6.25a-d. Wegener granulomatosis. Plain SE T1 in the axial plane (a), Gd-DTPA SE T1 in the sagittal (b) and axial plane (c-d). Hypointense mildly enhancing submucosal localizations of the disease are identified as pseudomasses (at the level of the soft palate, tonsillar fossa, nasal septum, and posterior tip of the middle and inferior turbinates) (white arrows). Plaque-like submucosal thickening is seen along the right lateral nasal (black arrowhead) and nasopharyngeal wall (white arrowhead). Extensive involvement of masticator spaces is demonstrated by vivid enhancement of pterygoid muscles (black arrows)

Fig. 6.25a-d. Wegener granulomatosis. Plain SE T1 in the axial plane (a), Gd-DTPA SE T1 in the sagittal (b) and axial plane (c-d). Hypointense mildly enhancing submucosal localizations of the disease are identified as pseudomasses (at the level of the soft palate, tonsillar fossa, nasal septum, and posterior tip of the middle and inferior turbinates) (white arrows). Plaque-like submucosal thickening is seen along the right lateral nasal (black arrowhead) and nasopharyngeal wall (white arrowhead). Extensive involvement of masticator spaces is demonstrated by vivid enhancement of pterygoid muscles (black arrows)

(Nishino et al. 1993; Provenzale and Allen 1996; Marsot-Dupuch et al. 2002). CT detection is mainly based on effacement of adjacent fat tissue planes; however, the limited contrast resolution of this technique makes discrimination between lesions and adjacent muscular structures very difficult to achieve. This information can be obtained with MR, whereby a granulomatous lesion exhibits hypointense signal on TSE T2 and plain SE T1 sequences. Contrast enhancement ranges between mild inhomogeneous (Muhle et al. 1997) to bright (Provenzale and Allen 1996). Differential diagnosis of orbital pseudotumoral lesions encompasses a long list of disease entities, including fungal in b a c

Fig. 6.26. Wegener granulomatosis. TSE T2 in the coronal plane. Bilateral orbital pseudomasses (arrows), extraconal on the left, intraconal on the right, where the lesion contacts the optic nerve

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