Histopathology of brain AVMs part I: microhemorrhages and changes in the nidal vessels

Clinical applications of arterial spin labeling of the intracranial compartment in vascular anomalies-A case-based review

Arterial spin labeling (ASL) is a magnetic resonance perfusion technique that allows for quantification of cerebral blood flow (CBF) without the use of contrast or radiation. Several applications of ASL have been described in diagnosis of strokes and stroke mimics, intracranial tumors, and other conditions. Various vascular anomalies exhibit specific CBF patterns that correlate with different signal intensities on ASL. In this case-based review, we demonstrate the utility of ASL in diagnosis and surveillance of vascular anomalies in the intracranial compartment.

Hemodynamic and Anatomical Factors in Arteriovenous Malformation Clinical Presentation: 45 Case Studies

BACKGROUND

Hemodynamic factors have been implicated in hemorrhage from cerebral arteriovenous malformations (AVMs). The goal of this endovascular study is to analyze the hemodynamic variability in AVM feeders in a balanced group of ruptured and unruptured AVMs of various sizes and at both superficial and deep locations.

METHODS

We monitored feeder artery pressure (FP) using microcatheters in 45 patients with AVMs (16 with hemorrhage, 29 without) during superselective angiography and AVM embolization.

RESULTS

Mean FP was 49 mm Hg. Significant determinants of FP were the systemic pressure (p < 0.001), AVM size (p = 0.03), and the distance of the microcatheter tip from the Circle of Willis (p = 0.06), but not the presence of hemorrhage, patient age, or feeder artery diameter. The FP in ruptured AVMs was 7 mm Hg higher than in unruptured ones (53.8 mm Hg vs. 47.1 mm Hg, p = 0.032). The presence or absence of venous outflow stenosis and the position of the AVM nidus (superficial or deep to the cortical surface) were important anatomical predictors of AVM presentation.

CONCLUSION

The pressure in the feeding artery supplying an AVM is the result of factors which include the systemic arterial pressure, the size of the AVM nidus, and the distance of the AVM from the Circle of Willis. The correlation between these variables makes it difficult to study the risk of hemorrhage as a function of a single factor, which may account for the variation in the conclusions of previous studies.

Cellular loci involved in the development of brain arteriovenous malformations

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a role of pericytes and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis.

Ischemia-induced inflammation in arteriovenous malformations

OBJECTIVE

The pathophysiology of development, growth, and rupture of arteriovenous malformations (AVMs) is only partially understood. However, inflammation is known to play an essential role in many vascular diseases. This feasibility study was conducted to investigate the expression of enzymes (cyclooxygenase 2 [COX-2] and NLRP3 [NOD-, LRR-, and pyrin domain–containing protein 3]) in the AVM nidus that are essential in their inflammatory pathways and to explore how these influence the pathophysiology of AVMs.

METHODS

The study group comprised 21 patients with partially thrombosed AVMs. The cohort included 8 ruptured and 13 unruptured AVMs, which had all been treated microsurgically. The formaldehyde-fixed and paraffin-embedded samples were immunohistochemically stained with a monoclonal antibody against COX-2 and NLRP3 (COX-2 clone: CX-294; NLRP3: ab214185). The authors correlated MRI and clinical data with immunohistochemistry, using the Trainable Weka Segmentation algorithm for analysis.

RESULTS

The median AVM volume was 2240 mm3. The proportion of NLRP3-positive cells was significantly higher (26.23%–83.95%), compared to COX-2 positive cells (0.25%–14.94%, p < 0.0001). Ruptured AVMs had no higher expression of NLRP3 (p = 0.39) or COX-2 (p = 0.44), compared to nonruptured AVMs. Moreover, no patient characteristics could be reported that showed significant correlations to the enzyme expression.

CONCLUSIONS

NLRP3 consistently showed an approximately 10-fold higher expression level than COX-2, making the inflammatory process in AVMs appear to be mainly associated with ischemic (NLRP3)–driven rather than with mechanical (COX-2)–driven inflammatory pathways. No direct associations between NLRP3 and COX-2 expression and radiological, standard histopathological, or patient characteristics were found in this cohort.

Orbital Vascular Anomalies: A Nomenclatorial, Etiological, and Nosologic Conundrum

PURPOSE

Vascular anomalies are a heterogeneous group of disorders that frequently present in the periorbital region. They encompass 2 broad entities: vascular tumors, which possess a proliferative endothelium, and vascular malformations, which are basically localized defects of vascular morphogenesis. The primary goal of this review was to address inaccurate or controversial terminology in the oculoplastic literature concerning orbital and periorbital vascular anomalies and to categorize these lesions in an abridged and simplified hierarchical list that adheres as much as possible to the most recent (2018) iteration for the classification of vascular lesions proposed by the International Society for the Study of Vascular Anomalies (ISSVA). The secondary goal of this review was to review and update information regarding the genetic underpinnings of vascular anomalies and the downstream signaling pathways that are subsequently affected as a result of these genetic errors.

METHODS

A literature review was conducted in PubMed, MEDLINE, PubMed Central, National Center for Biotechnology Information Bookshelf, and Embase for several related keywords including "vascular anomalies, vascular malformations, vascular tumors, and cavernous venous malformation," both with and without adding the keywords "eyelid," "orbital," and "periorbital." In addition, a detailed search was conducted for controversial or obsolete keywords like "cavernous hemangioma," "lymphangioma," and "varices," again in their systemic and orbital/periorbital context.

RESULTS

Crucial issues in the 2018 ISSVA classification regarding the proper categorization of orbital vascular anomalies, particularly venous lesions, were critically evaluated and revised, and a regional, simplified, and abridged modification of the ISSVA 2018 classification was proposed.

CONCLUSIONS

Interdisciplinary and intradisciplinary dialogue concerning orbital vascular anomalies is seriously compromised due to the lack of a unanimous agreement on terminology and the absence of a unified classification concept system. The authors recommend that oculoplastic surgeons adopt ISSVA terminology whenever technically possible and scientifically sound. However, they also propose modifying the ISSVA 2018 classification specifically to adapt to the peculiarities of vascular anomalies in the periorbital region. At present, the simplified classification proposed here is a preliminary first step towards managing patients with orbital vascular anomalies with greater diagnostic and therapeutic precision, until such time in the future when the entire genetic makeup of orbital vascular anomalies is more completely elucidated. Optimistically, this could pave the way for a more robust classification and the ultimate therapeutic cure.