Teaching Neuroimages: Inflammatory CAA

Excerpt

Inflammatory cerebral amyloid angiopathy (CAA) includes a spectrum of inflammatory diseases with similar clinical and imaging features, e.g. CAA-related inflammation (CAA-ri) and Aβ-related angiitis (ABRA). The CAA-ri is histologically characterized by focal accumulation of amyloid-β (Aβ) in leptomeningeal and parenchymal blood vessels associated with segmental perivascular inflammatory infiltrates and ABRA by the presence of intramural granulomas and regions of vessel wall destruction [1, 2]. Patients with inflammatory CAA typically present with rapid cognitive decline, focal neurologic deficits, headache, and/or seizures. Diagnostic criteria have recently been proposed for CAA-ri (Table 1; [5, 6]). The differential diagnosis of inflammatory CAA includes posterior reversible encephalopathy syndrome (PRES), acute disseminated encephalomyelitis (ADEM), reversible cerebral vasoconstriction syndrome (RCVS), chronic hypertensive encephalopathy, primary angiitis of the central nervous system (PACNS), autoimmune encephalitis, malignancies (such as primary neoplasms, CNS lymphoma and carcinomatous meningitis) and infections (especially progressive multifocal leukoencephalopathy). Inflammatory CAA is characterized by patchy or confluent T2 or fluid attenuation inversion recovery (FLAIR) hyperintensity which is usually asymmetric with or without leptomeningeal or parenchymal enhancement on magnetic resonance (MR) imaging. Infarcts are lacking and the edema is confluent, differentiating it from PACNS. Vascular imaging findings can also help differentiate PACNS and inflammatory CAA where PACNS can produce a pattern of multifocal narrowing and irregularity of middle to distal cerebral arteries. The edema can be unifocal or multifocal but is typically asymmetric when multifocal, distinguishing it from PRES [5]. Chronic hypertensive encephalopathy, also known as hypertensive microangiopathy, can be excluded based on patient history, examination, and imaging studies, which typically results in microhemorrhages in the basal ganglia, pons, and cerebellum. Vascular and nonvascular imaging findings can help differentiate inflammatory CAA and RCVS. The RCVS is a clinical and radiologic syndrome characterized by the hyperacute onset of severe headache and reversible segmental vasoconstriction of the cerebral arterial vasculature with either normal neuroimaging study or watershed infarct/vasogenic edema, differentiating it from inflammatory CAA [7]. This article describes the magnetic resonance imaging (MRI) spectrum in three men with histologically verified CAA-related inflammation and one woman with ABRA (Table 2) (Fig. 1). The MRI shows multifocal subcortical edema with U‑fiber involvement (Figs. 2 and 3). It also shows multiple cortical and subcortical microbleeds (Figs. 2, 3 and 4); however, only some areas with microbleeding show subcortical edema. There is faint leptomeningeal contrast enhancement in all patients (Figs. 2, 3 and 5). Interestingly and not unreported, one patient with a CAA-ri showed an enhancing parenchymal lesion (Fig. 4) and the ABRA patient also showed enhancing basal ganglia lesions (Fig. 5; [2‐4]). Characteristic are a subcortical edema with U‑fiber involvement in regions with microbleeding and a faint leptomeningeal enhancement. The parietal lobes are preferentially involved. CAA-related inflammation and ABRA cannot be distinguished clinically or on MRI. If the enhancing basal ganglia lesions found in patients with pathologically confirmed CAA-ri, since the basal ganglia are tipically devoid of amyloid, PCNSV should be considered in the differential diagnosis. In the latter case, PACNS is a relevant differential diagnosis.

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