Cliniconeuropathologic correlations show astroglial albumin storage as a common factor in epileptogenic vascular lesions

Abstract

Purpose: Intracerebral vascular malformations including cavernous angiomas (CAs) and arteriovenous malformations (AVMs) are an important cause of chronic pharmacoresistant epilepsies. Little is known about the pathogenetic basis of epilepsy in patients with vascular malformations. Intracerebral deposits of iron-containing blood products have been generally regarded as responsible for the strong epileptogenic potential of CAs. Here, we have analyzed whether blood-brain barrier (BBB) dysfunction and subsequent astrocytic albumin uptake, recently described as critical trigger of focal epilepsy, represent pathogenetic factors in vascular lesion-associated epileptogenesis.

Methods: We examined the correlation between hemosiderin deposits, albumin accumulation, and several clinical characteristics in a series of 80 drug-refractory epilepsy patients with CAs or AVMs who underwent surgical resection. Analysis of clinical parameters included gender, age of seizure onset, epilepsy frequency, duration of epilepsy before surgery, and postoperative seizure outcome classification according to Engel class scale. Hemosiderin deposits in the adjacent brain tissue of the vascular lesion were semiquantitatively analyzed. Fluorescent double-immunohistochemistry using GFAP/albumin costaining was performed to study albumin extravasation.

Key findings: Our results suggest that a shorter duration of preoperative epilepsy is correlated with significantly better postsurgical outcome (p < 0.05), whereas no additional clinical or neuropathologic parameter correlated significantly with the postsurgical seizure situation. Intriguingly, we observed strong albumin immunoreactivity within the vascular lesion and in perilesional astrocytes (57.65 ± 4.05%), but not in different control groups.

Significance: Our present data on albumin uptake in brain tissue adjacent to AVMs and CAs suggests BBB dysfunction and accumulation of albumin within astrocytes as a new pathologic feature potentially associated with the epileptogenic mechanism for vascular lesions and provides novel therapy perspectives for antiepileptogenesis in affected patients.

Figure 1

Representative histopathologic and neuroradiologic findings in patients with cavernous angiomas and arteriovenous malformations. Cavernous angiomas (CAs) are composed of thin, endothelium-lined vascular channels without muscular layers (Aa–c, scale bar = 200 μm, patient ID No. 61). Arterial vessels are absent (Aa: elastica-van Gieson staining). Usually, the sinusoidal blood cavities lie back-to-back and no brain tissue is present between the blood vessels. Prussian blue staining shows abundant intraparenchymal hemosiderin deposits in the vicinity of the lesion (Ab). GFAP-immunohistochemistry reveals strong reactive astrogliosis (Ac). Coronal T₂-weighted fast spin echo (Ba), axial fluid-attenuated inversion recovery (FLAIR) fast spin echo (Bb) and axial contrast-enhanced T₁-weighted spin echo images show a CA in the right inferior frontal gyrus. The oblong CA matrix is surrounded by hemosiderinladen brain parenchyma. Arteriovenous malformations (AVMs) are characterized by abnormal blood vessels with variable size and configuration (Ca–c, scale bar = 200 μm, patient ID No. 8). Different amounts of thick-walled arterial elements with parts of the tunica media and frequently dispersed fractions of the lamina elastica interna can be observed near thin, amuscular venous walls and transitory shunt vessels (Ca: elastica-van Gieson staining). Hemosiderin deposits are generally less abundant than in CAs (Cb: Prussian blue staining). Intervening brain tissue is a further feature of AVMs (Cc: GFAP-immunohistochemistry). On radiological evaluation, non–space-occupying lesions with tubular or rete-like “flow void” structures may be visible (Da–b, coronal and sagittal T₂-weighted MRI). Digital subtraction angiography (DSA) shows feeding arteries (Dc). Epilepsia © ILAE

Figure 2

Histopathologic findings in vascular malformations associated with focal cortical dysplasia type IIIc. In three patients (ID No. 12, 34, and 48) vascular malformation was associated with cortical dyslamination. H&E staining shows an occipital arteriovenous malformation and adjacent cortex (A, patient ID No. 12, scale bar = 400 μm,). Neuronal nuclei immunohistochemistry reveals microcolumnar (radial) dyslamination in the neocortex below the vascular lesion (B, scale bar = 400 μm; C, scale bar = 200 μm). Abundant microcolumns with more than eight neurons aligned in a vertical direction can be observed (arrows). VM, vascular malformation. Epilepsia © ILAE

Figure 3

Clinical parameters and hemosiderin deposits. Statistical analysis revealed no significant differences between epilepsy patients with either CA or AVM in gender, age at epilepsy onset, age at surgery (A), and outcome (B, p = 0.472, chi-square test). In contrast, higher amounts of hemosiderin deposits were present in patients with CA than in patients with AVM (C, p = 0.002, chi-square test). Localizations of the vascular lesions are shown in D. ^aFisher’s two-sided exact test. ^bUnpaired t-test. CA, cavernous angioma; AVM, arteriovenous malformation; f, female; m, male; nc, not classifiable. Epilepsia © ILAE

Figure 4

GFAP/albumin fluorescent double-immunohistochemistry in epilepsy patients with vascular malformations and different controls. Presence of GFAP-reactive astrocytes and albumin-reactive deposits was analyzed in biopsy specimens from patients with vascular malformations and drug-refractory epilepsy (A), patients with vascular malformations but absence of epilepsy (B), patients with epilepsy due to a focal cortical dysplasia type IIa (C), and in autopsy specimens from patients without cerebral pathology (D). Reactive astrocytes (arrowheads in column a) and intravasal albumin immunoreactivity (arrows in column b) were observed in all patients. In contrast, combined images (column c) revealed only in patients with vascular malformations and epilepsy colocalization of immunoreactivity (circles in Ac). Scale bar = 50 μm. Epilepsia © ILAE