Microanatomía de las malformaciones arteriovenosas: consideraciones quirúrgicas / Arteriovenous malformation microanatomy: surgical considerations

Las malformaciones arterovenosas (MAV) son una patología complicada que plantea importantes dilemas en su tratamiento. La cirugía directa constituye una de las pricipales armas terapéuticas y, para su correcta realización, es necesario conocer la arquitectura y microanatomía de las (MAV). Estas se componen de 3 partes: porción aferente o arterial, nido y porción eferente o venosa. Se describen las características de lcada una de estas partes y las maniobras quirúrgicas que en experiencia del autor son útiles para la resección quirúrgica. Se mencionan las posibles complicaciones que pueden sobrevenir durante la cirugía y como intentar solucionarlas. Se enfatiza la necesidad de evaluar lo más exhaustivamente posible la resonancia magnética y la angiografía preoperatorias para elegir la mejor estrategia quirúrgica. Palabras clave: cirugía, malformaciones arteriovenosas, microanatomía.

Arterio-venous malformations (AVM) are a complicated pathology that raise important dilemmas in their treatment. Direct surgery is one of the principal therapeutic options and, for its correct accomplishment it is necessary to know their architecture and microanatomy. They consist of 3 portions: afferent or arterial, nest and the efferent or venous. The characteristics of each one of them and the surgical steps that, in the experience of the author, are useful for the surgical resection are described. The possible complications that can appear during surgery are mentioned and also how to solve them. The need to evaluate, as exhaustively as possible, magnetic resonance images and preoperative angiography, to choose the best surgical strategy is emphasized. Key words: arterovenous malformations, microanatomy, surgery.

Ultrastructure of perinidal capillaries in cerebral arteriovenous malformations.

OBJECTIVE: The ultrastructure of perinidal capillaries in cerebral arteriovenous malformations (AVMs) was examined to clarify their pathomorphological features. METHODS: Fifteen AVM specimens were dissected and divided into perinidal and intranidal groups and processed for ultrastructural study immediately after surgical removal. Eleven of the patients had presented with hemorrhage. Tissue from four normal controls was also studied. Electron microscopy was used to compare features of the blood-brain barrier and endothelial cells (ECs) of capillaries in perinidal, intranidal, and controls. RESULTS: Perinidal capillaries demonstrated abnormal ultrastructure of the blood-brain barrier with no basement membranes and astrocytic foot processes. ECs had fenestrated luminal surfaces. Large gaps were observed at endothelial intercellular junctions. ECs contained numerous filopodia, large numbers of cytoplasmic processes, numerous micropinocytotic vesicles, and the cytoplasm contained more filaments than those observed in controls. Pericytes were rich in pinocytotic vesicles, vacuoles, and filaments. Their processes were in close contact with ECs. Weibel-Palade bodies were present in perinidal ECs. CONCLUSION: The absence of blood-brain barrier components in perinidal capillaries may contribute to extravasation of red blood cells into the surrounding brain in the absence of major hemorrhage and explain the gliosis and hemosiderin occasionally seen around AVMs. Cellular differentiation and proliferation in perinidal capillaries should be included in a systematic study aimed at a better understanding of the mechanisms underlying the recurrence of surgically removed AVMs.

Ultrastructural changes in arteriovenous malformations after gamma knife surgery: an electron microscopic study.

OBJECT: The authors analyzed morphological alterations at the subcellular level by undertaking transmission electron microscopy in arteriovenous malformations (AVMs) after gamma knife surgery (GKS). METHODS: Histological, immunohistochemical, and electron microscopic investigations were performed in a series of pathological specimens obtained in seven patients. The patients harbored cerebral AVMs that had been previously treated with GKS and had suffered subsequent bleeding 10 to 52 months after treatment. Histological studies revealed spindle cell proliferation in the connective tissue stroma and in the subendothelial region of the irradiated AVM vessels. Electron microscopy demonstrated different ultrastructural characteristics of this spindle cell population. There were cells with a smooth-edged oval nuclei surrounded by massive bundles of collagen fibers in the extracellular matrix. Other cells with the same nuclear morphology contained abundant intracytoplasmic filaments. Nuclear deformation was connected to a fibrillary system developed within the cytoplasm, and peripheral attachment sites were related to an extracellular layer of basement membrane-like material arranged parallel to the cell border. Also present were cells containing well-developed cisterns of rough endoplasmic reticulum and dense bodies at the periphery of the cytoplasm with folded, irregular nuclei. CONCLUSIONS: The ultrastructural and histological characteristics of the spindle cell population in the GKS-treated AVMs are similar to those designated as myofibroblasts in wound healing processes and pathological fibromatoses. Because similar cell modifications have not been demonstrated in control nonirradiated AVM specimens, these myofibroblasts may contribute to the shrinking process and final occlusion of AVMs after radiosurgery.

Angioganglioglioma: a transitional form between angioglioma and gangioglioma?

The authors describe for the first time an unusual cerebral tumor with unique clinical history, composed of 3 components: pilocytic astrocytoma, vascular proliferations similar to those described as arteriovanous malformations, and a neoplastic ganglion component. These three components were intimately entangled and created the tumor mass. Thus the authors propose the term angioganglioglioma for this entity. The relation to the historically defined anglioglioma and tumors related to ganglioglioma and dysembryoplastic neuroepithelial tumor is discussed. The authors believe that this lesion, in regard to the clinical presentation (long course of the disease, clinical symptoms), is closely associated with ganglioglioma and, with other morphological features, also to angioglioma. Further, it may constitute a new distinct clinicopathological entity with neoplastic and hamartomatous features.

Cerebral vascular abnormalities in a murine model of hereditary hemorrhagic telangiectasia.

BACKGROUND AND PURPOSE: Hereditary hemorrhagic telangiectasia type 1 (HHT1) is an autosomal dominant vascular dysplasia caused by mutations in the endoglin gene and characterized by dilated vessels and arteriovenous malformations (AVMs). To understand the etiology of this disorder, we evaluated the cerebral vasculature of endoglin heterozygous (Eng+/-) mice, which represent the only animal model of HHT1. METHODS: The cerebral vasculature of Eng+/- and Eng+/+ mice from C57BL/6 (B6) and 129/Ola (129) strains with a differential susceptibility to HHT1 was studied with corrosion casting. Casts were observed by scanning electron microscopy to detect malformations and evaluate arterial diameters and orientation of endothelial nuclei. Measurements were taken to assess relative constriction at arteriolar branching points and downstream relative dilatation. RESULTS: Three of 10 Eng+/- mice demonstrated abnormal vascular findings including AVMs, while none of 15 Eng+/+ mice did. The incidence of relative constriction at arteriolar branching points was significantly less in both Eng+/- groups than in their Eng+/+ counterparts. The occurrence of relative dilatation was significantly greater in B6-Eng+/- than in B6-Eng+/+ mice. Endothelial nuclei were significantly rounder and deviated more from the direction of blood flow in Eng+/- than in Eng+/+ mice. CONCLUSIONS: Eng+/- mice showed significant structural alterations in cerebral blood vessels, indicating that the level of endoglin on endothelium is critical for maintenance of normal vasculature. Since endoglin haploinsufficiency is associated with HHT1, such changes in arteriolar structures might occur in HHT1 patients and predispose them to AVMs and their sequelae.