Ultrastructural pathological features of cerebrovascular malformations: a preliminary report

Variations in structural protein expression and endothelial cell proliferation in relation to clinical manifestations of cerebral cavernous malformations

OBJECTIVE

Cerebral cavernous malformations (CCMs) are associated with hemorrhagic proliferation of endothelial-lined vascular caverns, resulting in hemorrhagic stroke, epilepsy, and other neurological manifestations. We hypothesize that structural protein expression and endothelial cell proliferation markers within CCM lesions are different in the setting of various clinical manifestations.

METHODS

The percentage of immunohistochemically stained caverns positive for collagen IV, fibronectin, laminin, alpha-smooth muscle actin, myosin, and smoothelin and the percentage of dividing endothelial cells within caverns were determined in 36 excised CCM surgical specimens. These were compared in CCMs with different multiplicity, location, and size in patients of different age, sex, seizure status, and hemorrhage status.

RESULTS

Comparisons of seven lesion features and clinical manifestations with the fraction of caverns containing the structural proteins studied and endothelial cell proliferation demonstrated no significant differences. A possible exception was the difference (P < 0.05) in the fraction (mean +/- standard deviation) of positively stained caverns for collagen IV between adult (0.63 +/- 0.39) and pediatric patients (0.87 +/- 0.21) as well as fewer caverns with laminin expression in older patients. These trends did not sustain significance with Bonferroni's correction for multiple comparisons.

CONCLUSION

The fraction of caverns containing the particular structural proteins studied and endothelial cell proliferation within caverns are not correlated with particular lesion features and clinical manifestations that were investigated in CCMs. The possible fewer fractions of caverns containing collagen IV and laminin in adult lesions compared with pediatric lesions may have implications for lesion regression and quiescence with age.

Mutations in apoptosis-related gene, PDCD10, cause cerebral cavernous malformation 3

OBJECTIVE

To identify the CCM3 gene in a population of 61 families with a positive family history of cerebral cavernous malformations (CCM), 8 of which had suggestive linkage to the CCM3 locus.

METHODS

We searched for mutations within the CCM3 interval using a high-throughput screening technique, temperature-gradient capillary electrophoresis. Mutations detected by this device were subsequently sequenced, and the results were analyzed.

RESULTS

A recent study by Bergametti et al. established Programmed Cell Death 10 (PDCD10) as the gene responsible for CCM3. We hereby confirm PDCD10 as the CCM3 gene by reporting four novel mutations in 61 CCM families. Two of these mutations were identical and produced a stop codon in exon 7. Another two resulted in frameshift mutations in exon 6, although the mutations occurred at different points along the exon. The last mutation caused a frameshift in exon 9. Of note, mutations in these families completely cosegregated with the trait. Three of the five families had prior linkage data suggestive of the CCM3 locus, whereas the remaining two were identified in index patients with a positive family history but no linkage data.

CONCLUSION

Our data establish PDCD10 as the gene responsible for CCM in families linking to the CCM3 locus. The discovery of the third gene involved in inherited forms of CCM, after KRIT1 and Malcavernin, is an important step toward dissecting the molecular pathophysiology of this disease.

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.

Cerebral cavernous malformation: new molecular and clinical insights

Cerebral cavernous malformation (CCM) is a vascular malformation causing neurological problems, such as headaches, seizures, focal neurological deficits, and cerebral haemorrhages. CCMs can occur sporadically or as an autosomal dominant condition with variable expression and incomplete penetrance. Familial forms have been linked to three chromosomal loci, and loss of function mutations have been identified in the KRIT1/CCM1, MGC4607/CCM2, and PDCD10/CCM3 genes. Recently, many new pieces of data have been added to the CCM puzzle. It has been shown that the three CCM genes are expressed in neurones rather than in blood vessels. The interaction between CCM1 and CCM2, which was expected on the basis of their structure, has also been proven, suggesting a common functional pathway. Finally, in a large series of KRIT1 mutation carriers, clinical and neuroradiological features have been characterised. These data should lead to more appropriate follow up, treatment, and genetic counselling. The recent developments will also help to elucidate the precise pathogenic mechanisms leading to CCM, contributing to a better understanding of normal and pathological angiogenesis and to the development of targeted treatment.

Neuronal expression of the Ccm2 gene in a new mouse model of cerebral cavernous malformations

Cerebral cavernous malformations are vascular defects of the central nervous system consisting of clusters of dilated vessels that are subject to frequent hemorrhaging. The genes mutated in three forms of autosomal dominant cerebral cavernous malformations have been cloned, but it remains unclear which cell type is ultimately responsible for the lesion. In this article we describe mice with a gene trap insertion in the Ccm2 gene. Consistent with the human phenotype, heterozygous animals develop cerebral vascular malformations, although penetrance is low. Beta-galactosidase activity in heterozygous brain and in situ hybridization in wild-type brain revealed Ccm2 expression in neurons and choroid plexus but not in vascular endothelium of small vessels in the brain. The expression pattern of Ccm2 is similar to that of the Ccm1 gene and its interacting protein ICAP1 (Itgb1bp1). These data suggest that cerebral cavernous malformations arise as a result of defects in the neural parenchyma surrounding the vascular endothelial cells in the brain.

CCM2 Expression Parallels That of CCM1

Background and Purpose— Mutations in CCM2 (MGC4607 or malcavernin) cause familial cerebral cavernous malformation (CCM), an autosomal dominant neurovascular disease. Both the function of this molecule and the pathogenesis of the disease remain elusive.

Methods— We analyzed the mRNA expression of Ccm1 and Ccm2 in the embryonic and postnatal mouse brain by in situ hybridization. Subsequently, we generated CCM2-specific polyclonal antibodies and tested their specificity using transient transfection experiments in various cell lines. We then investigated CCM2 protein expression in cerebral and extracerebral tissues by Western blot analysis as well as immunohistochemistry and compared these results with CCM1 (KRIT1) protein expression.

Results— In situ analysis shows similar temporal and spatial expression patterns for Ccm1 and Ccm2, although Ccm1 expression appears more widespread. Immunohistochemical analysis shows that CCM2 is expressed in various human organs, most noticeably in the arterial vascular endothelium. As is the case with CCM1, CCM2 is not expressed in other vascular wall elements such as smooth muscle cells or the venous circulation. Within cerebral tissue, it is also expressed in pyramidal neurons, astrocytes, and their foot processes. In extracerebral tissues, CCM2 is present in various epithelial cells necessary for blood-organ barrier formation.

Conclusions— CCM1 and CCM2 have similar expression patterns during development and postnatally thereafter. Given the fact that the disease phenotypes caused by mutations in either gene are clinically and pathologically indistinguishable, the significant overlap in expression pattern supports the hypothesis that both molecules are involved in the same pathway important for central nervous system vascular development.

Genetics of cerebral cavernous malformations

The past few years have seen rapid advances in our understanding of the genetics and molecular biology of cerebral cavernous malformations (CCM). This article summarizes the recent cloning of the CCM1, CCM2, and CCM3 genes, which are responsible for autosomal dominant CCM, and also describes current hypotheses for their roles in integrin and p38 mitogen-activated protein kinase- mediated regulation of angiogenesis. A mouse model of CCM has been generated by mutation of the Ccm1 gene, and it indicates a role for that protein in arterial development. Future studies will probably focus on integration of data from each of the three CCM genes into a single model of the pathogenesis of cavernous malformation.

Ultrastructural characteristics of hemorrhagic, nonhemorrhagic, and recurrent cavernous malformations

OBJECT

Ultrastructural characteristics of hemorrhagic, nonhemorrhagic, primary, and recurrent central nervous system cavernous malformations (CMs) were examined in an attempt to clarify their pathological mechanisms.

METHODS

Thirteen specimens (nine from samples of CMs and four from healthy control tissue) were processed for ultrastructural study immediately after surgical or postmortem removal, by fixation in glutaraldehyde/formalin and postfixation in OsO4. Transmission electron microscopy was used to examine the vascular walls, endothelium, subendothelium, and cytoplasmic organelles. The vascular walls in CMs demonstrated abnormal ultrastructure with no basement membranes and astrocytic foot processes. Pericytes were rarely seen. Single-layer lining endothelial cells showed fenestrated luminal surfaces. Large gaps were observed at intercellular junctions between endothelial cells, and large vesicles with extremely thin plasma membranes bordering the lumen were common in the lesions that had previously hemorrhaged. Endothelial cells of recurrent CMs had more Weibel-Palade bodies, filopodia, cytoplasmic processes, micropinocytotic vesicles, and filaments than those in primary lesions and normal control tissues.

CONCLUSIONS

The absence of the blood-brain barrier, normal supporting wall structure, and large vesicles bordering the lumen of CM vessels may explain leakage of red blood cells into surrounding brain in the absence of major hemorrhage. Proliferation of residual abnormal endothelial cells may contribute to the recurrence of surgically removed CMs.

Characterization of the Integrin αvβ3 in Arteriovenous Malformations and Cavernous Malformations

BACKGROUND

Alpha V beta 3 (alphavbeta3) is an integrin specifically expressed on the endothelial cells of central nervous system (CNS) neoplasms. However, no data exist on the expression of alphavbeta3 in vascular malformations of the CNS. In this study, we investigate the expression of alphavbeta3 in arteriovenous malformations (AVMs) and cavernous malformations (CMs).

METHOD

Frozen samples of AVMs from 12 patients and CMs from 5 patients were obtained intraoperatively. Once the final pathology had been confirmed, immunohistochemistry was performed using an antibody to the integrin alphavbeta3. The alphavbeta3 expression pattern was graded according to the percentage of positively staining vessels.

RESULTS

Ten of 12 AVMs demonstrated alphavbeta3 immunopositivity. Six of these 10 AVMs had moderate or strong staining. Most notably, 5 of the 6 moderate or strongly staining AVMs came from patients 22 years of age or younger. Four of these 6 AVMs had previously been embolized. None of the cavernous malformations demonstrated alphavbeta3 immunopositivity.

DISCUSSION

alphavbeta3 may contribute to the formation of AVMs in younger patients. alphavbeta3 may also provide a potential therapeutic target. The lack of alphavbeta3 expression in cavernous malformations, despite their high vascular densities, suggests that the pathophysiology of their formation differs from that of AVMs.

Thrombus and encapsulated hematoma in cerebral cavernous malformations

Thrombi, encapsulated hematomas, and granulation tissue are frequently seen in cerebral cavernous malformations (CCMs). We investigated the role that these histological changes play in repeated hemorrhages in CCMs as well as lesion growth, examining specimens of CCMs surgically harvested from 20 patients. The immunohistochemical study included thrombomodulin (TM) and endothelial cell protein C receptor (EPCR), which are important regulators of blood coagulation. Thick capsules, which contained blood degradation product, were seen in cases with encapsulated hematomas. Clusters of sinusoidal vessels were found outside of these thick capsules. Granulation tissue with inflammatory infiltrates and capillaries was seen in 4 cases with non-capsulated hematomas. Organizing thrombi were seen in sinusoidal vessels in 15 out of 20 cases. Factor VIII-related antigen staining demonstrated numerous capillaries in and around organizing thrombi and within the thickened vessel walls as well as in both the inner and outer sides of the hematoma capsule. TM and EPCR were positive in the endothelial cells of these capillaries, whereas they were negative in those of capillaries in the brain surrounding the lesions. Our study suggests that thrombosed sinusoidal blood vessels could gradually expand by repeated bleeding from numerous capillaries inside the wall and become encapsulated hematomas, and capillaries outside the thickened vessel wall could become sinusoidal blood vessels. Thrombosis within cerebral venules could be one of the causal factors of CCMs.

KRIT1/cerebral cavernous malformation 1 protein localizes to vascular endothelium, astrocytes, and pyramidal cells of the adult human cerebral cortex

OBJECTIVE

Mutations in KRIT1 cause familial cerebral cavernous malformation, an autosomal dominant disorder affecting primarily the central nervous system vasculature. Although recent studies have suggested that Krev-1 interaction trapped 1 (KRIT1) is a microtubule-associated protein that interacts with integrin cytoplasmic domain-associated protein-1alpha, the function of KRIT1 remains elusive.

METHODS

We used Western blotting and immunohistochemistry with specific KRIT1 polyclonal antibodies to investigate KRIT1 protein expression in diverse cerebral and extracerebral tissues.

RESULTS

Immunostaining demonstrates that although KRIT1 is expressed in a broad variety of human organs, it localizes to the vascular endothelium of each, specifically to capillaries and arterioles. KRIT1 antibody fails to stain fenestrated capillaries in the kidney, the liver, or the red pulp of the spleen, where endothelial cells do not to adhere to one another. In contrast, intense staining is observed in the thymus and the white pulp of the spleen, where specialized blood-organ barriers are formed. Other cell types, including various epithelia, cardiac myocytes, and hepatocytes, also stain with KRIT1.

CONCLUSION

Although KRIT1 expression is seen in every endothelium studied, cerebral cavernous malformation lesions are seen almost exclusively in the central nervous system, suggesting that additional cell type(s) contribute to the pathophysiology of cerebral cavernous malformations. Here, we demonstrate that KRIT1 is also present in cells and structures integral to the cerebral angiogenesis and formation of the blood-brain barrier, namely, endothelial cells and astrocytic foot processes, as well as pyramidal neurons in the cerebral cortex.

Mutational analysis of 206 families with cavernous malformations

OBJECT

A gene contributing to the autosomal-dominant cerebral cavernous malformation (CCM) phenotype, KRIT1 (an acronym for Krev Interaction Trapped 1), has been identified through linkage analysis and mutation screening. The authors collected blood samples from 68 patients with familial CCM and 138 patients with apparently sporadic CCM as well as from their families, in an effort to characterize the prevalence and spectrum of disease-causing sequence variants in the KRIT1 gene.

METHODS

The authors used single-strand conformational polymorphism analysis to identify genomic variants in KRIT1, which were sequenced to determine the specific mutation. Among 43 Hispanic-American kindreds who immigrated to the southwestern US from northern Mexico, 31 share an identical founder mutation. This Q455X mutation is found in 18 (86%) of 21 persons with a positive family history and in 13 (59%) of 22 persons with apparently sporadic CCM. This mutation was not found among 13 persons with CCM who were recruited from Mexico. These findings establish the key role of a recent founder mutation in Hispanic persons with CCM who live in the US. Although nearly all Hispanic families in the US in which there are multiple CCM cases linked to the CCM1 locus, only 13 of 25 non-Hispanic CCM-carrying families have displayed evidence of linkage to the CCM1 locus. Among these 13 families, the authors identified eight independent mutations in nine kindreds. They identified four additional mutations among 22 familial CCM kindreds with no linkage information, bringing the total number of independent mutations to 12. Inherited KRIT1 mutations were not detected among 103 non-Hispanic persons in whom a family history of CCM was rigorously excluded.

CONCLUSIONS

All mutations were nonsense mutations, frame-shift mutations predicting premature termination, or splice-site mutations located throughout the KRIT1 gene, suggesting that these are genetic loss-of-function mutations. These genetic findings, in conjunction with the clinical phenotype, are consistent with a two-hit model for the occurrence of CCM.

Giant cavernoma of the brain stem: value of delayed MR imaging after contrast injection

Cavernous angiomas are vascular malformations composed of slowly perfused, sinusoidal vessels which can be located in any part of the central nervous system. Whereas diagnosis is mostly straightforward in typical cases, some lesions may present in unusual locations or with unusual imaging characteristics. Because of the slow perfusion, contrast enhancement is not regarded as a characteristic imaging feature of cavernomas. We report a large brain stem cavernoma with signs of recent bleeding, in which the differential diagnosis against other mass lesions was facilitated by the demonstration of slow, but intense, contrast enhancement on MRI 1 h after contrast injection. We conclude that contrast enhancement in delayed images may contribute to a safe diagnosis of cavernous haemangiomas and should be performed in atypical cases.

Intracranial cavernous malformations

Cavernous malformations are commonly being recognized on CT and MR imaging in both asymptomatic and symptomatic patients. The diagnosis of CMs can often be made on MR imaging based on the characteristic morphology of the subacute and chronic blood products. An atypical appearance of a CM in the setting of a recent hemorrhage requires follow-up imaging to confirm the diagnosis. Deep CMs have a significant clinical event rate that justifies close follow up or surgical treatment if possible.

Differential gene expression in human cerebrovascular malformations

OBJECTIVE

We sought to identify genes with differential expression in cerebral cavernous malformations (CCMs), arteriovenous malformations (AVMs), and control superficial temporal arteries (STAs) and to confirm differential expression of genes previously implicated in the pathobiology of these lesions.

METHODS

Total ribonucleic acid was isolated from four CCM, four AVM, and three STA surgical specimens and used to quantify lesion-specific messenger ribonucleic acid expression levels on human gene arrays. Data were analyzed with the use of two separate methodologies: gene discovery and confirmation analysis.

RESULTS

The gene discovery method identified 42 genes that were significantly up-regulated and 36 genes that were significantly down-regulated in CCMs as compared with AVMs and STAs (P = 0.006). Similarly, 48 genes were significantly up-regulated and 59 genes were significantly down-regulated in AVMs as compared with CCMs and STAs (P = 0.006). The confirmation analysis showed significant differential expression (P < 0.05) in 11 of 15 genes (angiogenesis factors, receptors, and structural proteins) that previously had been reported to be expressed differentially in CCMs and AVMs in immunohistochemical analysis.

CONCLUSION

We identify numerous genes that are differentially expressed in CCMs and AVMs and correlate expression with the immunohistochemistry of genes implicated in cerebrovascular malformations. In future efforts, we will aim to confirm candidate genes specifically related to the pathobiology of cerebrovascular malformations and determine their biological systems and mechanistic relevance.

Relationship of nidal vessel radius and wall thickness to brain arteriovenous malformation hemorrhage

Cerebral (brain) arteriovenous malformations (BAVMs) are a tangle of disorganized vessels that are a rare cause of hemorrhagic stroke in the general population. Although clinical presentation of hemorrhage may be related to the structure of BAVM vessels, there has been no systematic quantitative analysis of BAVM vessel morphology. Histological sections of excised BAVM lesions were prepared from patients who presented with hemorrhage (n = 14) and from patients with no history of hemorrhage (n = 22). Mean values of radius and wall thickness in each section were determined. BAVM radii were 422+/-136 microm (mean +/- SD), minimum wall thickness (thinnest portion of the wall) was 54+/-14 microm; and the minimum thickness/radius ratio was 0.23+/-0.07. Greater vessel wall thickness was associated with hemorrhagic presentation (OR= 1.1; p = 0.046) after adjusting for feeding artery pressure. Because BAVM vessels from patients presenting with hemorrhage had thicker vessel walls, the search for structural properties predisposing BAVM rupture should be expanded beyond the morphological properties analyzed here.

Further study of CD31 protein and messenger ribonucleic acid expression in human cerebral vascular malformations

OBJECTIVE

In a previous study, we documented lower levels of immunoexpression of platelet endothelial cell (EC) adhesion molecule (CD31) in paraffin sections of cerebral cavernous malformations (CCMs), compared with arteriovenous malformations (AVMs) or normal brain tissue. We hypothesized that down-regulation of CD31 in CCMs might represent a distinctive phenotypic feature of ECs in this disease. To confirm this hypothesis, we further examined both protein and messenger ribonucleic acid (mRNA) expression of CD31, using immunohistochemical and in situ hybridization analyses, in fresh-frozen specimens of CCMs, AVMs, and control brain tissue.

METHODS

Fresh-frozen sections of four AVMs, five CCMs, and four control brain tissue specimens obtained from surgical resections were immunohistochemically stained with antibodies to von Willebrand factor and two distinct epitopes of CD31. In two AVMs, four CCMs, and three control brain tissue samples from the aforementioned group, the expression of CD31 mRNA was also examined by using in situ hybridization. Large (>100-microm) and small (<100-microm) vessels were counted and assessed for protein and mRNA expression.

RESULTS

In all tissues, ECs in the majority of vessels were immunopositive for CD31 with two distinct antibodies. CD31 mRNA was expressed in some but not all vessels in AVMs, CCMs, and control brain tissue. There were no statistically significant differences in CD31 protein or mRNA expression in CCMs, AVMs, and control brain tissue.

CONCLUSION

The expression of CD31 in CCMs can be underestimated in paraffin sections. There does not seem to be a unique phenotypic differentiation of CD31 expression in ECs of CCMs or AVMs, compared with control brain tissue.

The juxtaposition of a capillary telangiectasia, cavernous malformation, and developmental venous anomaly in the brainstem of a single patient: case report

OBJECTIVE AND IMPORTANCE

Capillary telangiectasias, cavernous malformations, and developmental venous anomalies are all vascular malformations that occur on the capillary-venous side of the cerebral circulation. The associations of capillary telangiectasias with venous malformations, cavernous malformations with venous malformations, and capillary telangiectasias with cavernous malformations have all been described; however, the association of all three lesions in a single patient is extremely rare.

CLINICAL PRESENTATION

A 52 year-old Caucasian woman presented to our clinic with an extended history of confusion, distorted visual perceptions, photophobia, neck pain, swallowing problems, and poor balance. The patient's examination was remarkable for difficulty concentrating, mild rotatory nystagmus, subtle decreased sensation over the left side of the face and body, and brisk reflexes. Review of the patient's magnetic resonance imaging examination demonstrated a cavernous malformation, a capillary telangiectasia, and a developmental venous anomaly located adjacent to one another in the brainstem.

INTERVENTION

Given the patient's complex constellation of symptoms and relatively mild neurological findings, it was difficult to ascribe any one of them to a specific vascular malformation. Conservative management of this patient's vascular malformations was decided upon.

CONCLUSION

Juxtaposition of these three different vascular lesions in the brainstem of an otherwise normal individual suggests a relationship among them. Although there are several theories that link similar associations through physiological mechanisms such as venous hypertension, we propose that a developmental event disrupting local capillary-venous pattern formation is a plausible alternative.

Vascular smooth muscle cell differentiation in human cerebral vascular malformations

OBJECTIVE

The pathogenesis of central nervous system vascular malformations likely involves the abnormal assembly, differentiation of vascular smooth muscle cells (VSMC), or both in association with dysmorphic vessel wall. We hypothesize that intracranial arteriovenous malformations (AVMs) and cerebral cavernous malformations (CCMs) exhibit distinct patterns of expression of molecular markers of differentiation and maturity of VSMCs. We further speculate that the unique VSMC phenotype in the different lesions is not necessarily maintained in cell culture.

METHODS

Paraffin-embedded sections of five AVMs, CCMs, and control brain tissues were stained immunohistochemically with antibodies to alpha-smooth muscle actin (alpha-SMA), myosin heavy chain, and smoothelin, a novel marker for contractile VSMC phenotype. Large (> or =100 microm) and small (<100 microm) vessels were counted and assessed for immunoexpression of each protein, then categorized according to expression of one or more of these markers. Cultured nonendothelial cells isolated from four other excised AVM and CCM lesions were assessed for immunoexpression of the same antibodies.

RESULTS

Alpha-SMA was universally expressed in all vessels in AVMs and in control brains. It was expressed in the subendothelial layer of 97% of large caverns and 85% of small caverns and in scattered intercavernous connective tissue fibrocytes in CCMs. Myosin heavy chain was expressed in the majority of brain and AVM vessels, except for normal veins, and in the subendothelial layer of more than half of the caverns in CCMs. Smoothelin expression was less prevalent in large vessels in AVMs than in control brains and was not found in any caverns in CCMs (large vessels in control brains, 40.9%; AVMs, 21.9%; CCMs, 0%; P < 0.0001). Cultured AVM and CCM nonendothelial cells expressed alpha-SMA, but myosin heavy chain was expressed weakly in cells from only one CCM. Smoothelin was negative in all cells.

CONCLUSION

We describe vessels with various stages of VSMC differentiation in AVMs and CCMs. The subendothelial layer of CCMs commonly expresses alpha-SMA and less commonly expresses myosin heavy chain. Expression of smoothelin was less prevalent in large AVM vessels than in normal brain, which may reflect the loss of contractile property associated with hemodynamic stress. It is difficult to evaluate VSMC differentiation in culture because of phenotypic change.

Ultrastructural and immunocytochemical evidence that an incompetent blood-brain barrier is related to the pathophysiology of cavernous malformations

OBJECTIVES

Cerebral cavernous malformations are linked to mutations of the KRIT1 gene at the CCM1 locus and to mutations at two other loci, CCM2 and CCM3, for which genes are not yet identified. There is little information regarding the function of KRIT1. Histological and immunocytochemical analysis of cavernous malformations have not shed much light on their pathophysiology.

METHODS

Morphological analysis of cavernous malformations was extended to the ultrastructural level by examining lesions from two patients by immunocytochemistry and electron microscopy.

RESULTS

The lesions consisted of endothelial lined vascular sinusoids embedded in a collagen matrix. Nuclei belonging to cells distinct from endothelial cells were rare. The basal lamina of the endothelial cells consisted focally of multiple layers. No tight junctions at endothelial cell interfaces were found; however, several examined endothelial cell interfaces demonstrated apparent gaps between endothelial cell processes where basal lamina was exposed directly to the lumen of the sinusoids. Heavy hemosiderin deposits were found underlying the vascular channels within microns of the basal lamina without evidence of disrupted vessels. No astrocytic foot processes were seen within lesions. Glial fibrillary acidic protein immunocytochemistry confirmed that astrocyte processes stopped at the border of the lesions.

CONCLUSIONS

The absence of blood-brain barrier components may lead to leakage of red blood cells into these lesions and the surrounding brain in the absence of major haemorrhage, thus accounting for the propensity of cavernous malformations to cause seizures. These data also raise the possibility that KRIT1 plays a part in the formation of endothelial cell junctions and expression of a mature vascular phenotype.

Expression of endothelial cell angiogenesis receptors in human cerebrovascular malformations

OBJECTIVE

To further understand the role of angiogenic growth factors in the development of cerebral cavernous malformations (CCMs) and arteriovenous malformations (AVMs), we investigated endothelial cell (EC) expression of receptors for vascular endothelial growth factor (VEGF) and angiopoietin systems in patients with surgically resected lesions.

METHODS

Paraffin-embedded sections of five AVMs, CCMs, and normal control brain tissue samples were stained immunohistochemically with antibodies to von Willebrand factor and CD31 (to characterize ECs) and angiogenesis growth factor receptors Flt-1 (VEGF-R1), Flk-1 (VEGF-R2), Tie-1, and Tie-2. We counted large and small vessels in each specimen, assessed each specimen's immunoexpression of each antigen, and analyzed differences between CCMs, AVMs, and the normal control brain tissue samples.

RESULTS

The ECs of CCMs, AVMs, and normal control brain tissue samples expressed the von Willebrand factor uniformly, but the ECs of CCMs were largely negative for CD31 (P < 0.05). Flk-1, Flt-1, and Tie-2 were not expressed in the control brain tissue samples. The proportion of immunopositive vessels to VEGF receptors Flk-1 and Flt-1 was significantly greater in AVMs and CCMs than in the control brain tissue samples (P < 0.05). Tie-2 in AVMs and CCMs was expressed in a higher percentage of immunopositive vessels than in the control brain tissue samples, but the difference was not statistically significant. Tie-1 was expressed in rare vessels of all lesion types and control brain tissue samples.

CONCLUSION

ECs of CCMs do not seem to express CD31 to the same extent that AVMs and normal brain tissue do. AVMs and CCMs show greater expression of VEGF receptors, but not of angiopoietin receptors, than normal brain tissue does.