Page 53 - The Vasculitides Volumes 2

Neuroimaging of the Vasculitides 29

75%, but specificity was 83%. Concentric homogeneous mural thickening, stenosis and
occlusion of the aorta and brachiocephalic branches are typical CDU features of GCA and
TAK [69, 85, 86], which may be differentiated from atherosclerotic disease by the absence of
plaque formation, concentric long segment involvement and location. Ultrasonography
revealed subtle mural changes characterized by a homogenous, circumferential mid-echoic
wall thickening within the subclavian and carotid arteries in the early stages of TAK
preceding abnormalities detected by CA [87], with overall greater wall thickness of the CCA
and ICA in the vasculitic vessels compared to controls. The CCA intima to medial thickness
ratio was increased in patients with TAK compared with normal control [88] yielding
respective sensitivity and specificity rates of 82% and 70%.

The wall diameters of common, frontal and parietal division of the superficial temporal
artery were significantly greater in patients with GCA than in symptomatic patients without
the disease as well as asymptomatic age-matched controls [89]. A hypoechoic halo
surrounding a patent vessel lumen was found in 73% of biopsy proven vasculitis patients but
not in symptomatic patients without GCA and asymptomatic controls. The histopathologic
finding of mural cellular infiltration did not correlate with a hypoechoic halo albeit attributed
to edema. The halo disappeared at a mean of 16 days following effective treatment.
Similar findings are present in the occipital arteries [90] although the sensitivity is less when
compared with the superficial temporal arteries. The halo examination is a useful exam for
symptomatic patients presenting with nuchal pain, occipital headache or occipital scalp
tenderness, especially when occipital artery involvement may be the only imaging
manifestation of the disease.

Conclusion

The neuroimaging evaluation of vasculitis may seem complex and nonspecific,
particularly for PACNS and the primary systemic autoimmune vasculitides. When all imaging
modalities including those that provide parenchymal, luminal and mural evaluation
are brought to bear on a given patient with suspected vasculitis, the entire constellation of
findings typically brings clarity to the situation. The largest single series of PACNS [35]
demonstrated that 77% of CT, 97% of MRI, 59% of MRA and 90% of CA studies were
ultimately positive in comparison to 62% of positive brain biopsies. Each individual modality
may be nonspecific, but the diagnosis of only a few patients will be missed by a concerted
neuroimaging evaluation. When imaging is combined with the clinical and laboratory results,
this diagnostic triad becomes more predictable even in the most difficult of clinical cases.

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