Arteriovenous malformations of the brain: a teratologic challenge

Spatial convergence of distant cortical regions during folding explains why arteries do not cross the sylvian fissure

OBJECTIVE

Cortical folding places regions that are separated by a large distance along the cortical surface in close proximity. This process is not homogeneous; regions such as the insular opercula have a much higher cortical surface distance (CSD) to euclidean distance (ED) than others. Here the authors explore the hypothesis that in the folded brain the CSD, and not the ED, determines regions of common irrigation, because this measure corresponds more closely with the distance along the prefolded brain, where the subarachnoid arterial vascular network starts forming.

METHODS

The authors defined a convergence index that compared the ED to the CSD and applied it to the cortical surface reconstruction of an average brain. They then compared cortical convergence to the irrigation patterns of major sulci and fissures of the brain, by assessing whether these structures were crossed or not crossed by arterial vessels in 20 fixed hemispheres.

RESULTS

The regions of highest convergence (top 1%) were clustered around the sylvian fissure, which is the only brain depression with high convergence values along its edges. Arterial crossings were commonly observed in every major sulcus of the brain, with the exception of the sylvian fissure, constituting a highly significant difference (p < 10-4).

CONCLUSIONS

Arteries do not cross regions of high convergence. In the adult brain the CSD, rather than the ED, predicts the regional irrigation pattern. The distant origin of the frontal and temporal lobes creates a region of high cortical convergence, which explains why arteries do not cross the sylvian fissure.

Cerebellar vascular hamartoma in a British Shorthair cat

Cerebellar vascular hamartoma was diagnosed in a 16-month-old cat following magnetic resonance imaging and incisional biopsy. The clinical features were consistent with the cerebellar site of the lesion accompanied by signs attributable to cerebellar herniation through the foramen magnum and increased intra-cranial pressure. A lesion of this type represents a previously unreported differential diagnosis for central nervous system lesions in young cats.

Expression of myosin heavy chain isoforms by smooth muscle cells in cerebral arteriovenous malformations

We have characterised the blood vessels found in normal cerebral vasculature and in arteriovenous malformations (AVMs), based on the expression of smooth muscle cell (SMC)-specific proteins. The marker proteins used were smooth muscle alpha-actin and four myosin heavy chain isoforms (SM1, SM2, SMemb and NMHC-A). Specimens of AVM obtained during surgery, and normal cerebral vessels from autopsy cases were studied immunohistochemically and compared. The arterial components of AVM contained an abundance of SMCs of the contractile phenotype, which were positive for alpha-actin, SM1 and SM2, but not for SMemb and NMHC-A. These components showed the same staining pattern as mature normal arteries. Two different types of abnormal veins were found in the AVM specimens: large veins with a thick and fibrous wall (so-called 'arterialised' veins) and intraparenchymal thin-walled sinusoidal veins. The former expressed alpha-actin, SM1, SM2, and SMemb, the latter expressed alpha-actin, SM1, and SM2. These marker expression patterns resembled those of normal cerebral arteries, and the results were compatible with arterialisation of the cerebral veins caused by arteriovenous shunting. However, the expression of SMemb was found only in the arterialised type of veins, not in the sinusoidal type or the arteries that had sustained abnormal blood flow in the AVMs. The thick-walled veins in the AVMs showed the same staining pattern as normal veins of dural plexus origin (large subarachnoid veins and dural sinuses). It is therefore possible to assume that they originated from the dural plexus, and extended into the brain during the formation of AVMs.

Surgical treatment of an intramedullary spinal cord hamartoma in a dog

A 9-year-old spayed female Golden Retriever was examined because of progressive hind limb lameness. Magnetic resonance imaging of the thoracic and lumbar portions of the vertebral column revealed a focal, contrast-enhancing, intramedullary spinal cord mass. The history, signalment, and magnetic resonance findings were suggestive of spinal cord neoplasia. A hemilaminectomy, durotomy, and longitudinal myelotomy were performed, and a 1 X 1-cm mass that contained numerous blood vessels was removed with blunt dissection. Results of histologic examination and immunohistochemical staining of the mass suggested that it was a hamartoma. The dog improved after surgery, with no evidence of a recurrence of clinical signs 14 months after surgery. Vascular malformations of the CNS in dogs include hamartomas, hemangiomas, angiomas, hemangioblastomas, meningocerebral hemangiomatosis, and arteriovenous malformations. A hamartoma is a non-neoplastic overgrowth of cells or an improper proportion of cells that are normally in the involved tissue. Although magnetic resonance imaging may be helpful in determining the extent of the lesion in dogs with vascular malforrmations, it cannot be used to distinguish neoplastic from non-neoplastic formations. Excision may result in a good outcome for dogs with an intramedullary spinal cord hamartoma.

The pathogenesis of diabetes-associated congenital malformations

Congenital malformations convey a major financial and social burden to society. Epidemiologic, clinical, and animal studies indicate that these malformations occur in early pregnancy, are influenced by an aberrant metabolic fuel milieu, and seem to result from a combination of more than one factor acting synchronously. Unfortunately, during the critical period of organogenesis, the pregnancy is hardly recognizable, making evaluation and study of relevant maternal embryonic parameters extremely difficult. Additionally, there are obvious limitations to human study for technical and ethical reasons. Animal experimentation, however, has demonstrated that these malformations can be produced in many vertebrates and are similar to those seen in humans. The mechanism for induction of dysmorphogenesis in experimental diabetic pregnancy has been shown to include generation of free oxygen radicals and are associated with alterations in the embryonic levels of arachidonic acid, prostaglandins, and myo-inositol. Most of the earlier experimental studies focused on defects at the level of the embryo excluding the extraembryonic membranes. Current investigations provide evidence that the yolk sac has an integral role in diabetic embryopathy. The experimental use of several different compounds, such as arachidonic acid, myo-inositol, and antioxidants, offers significant promise for the future in possibly serving as a pharmacologic prophylaxis against diabetic embryopathy.

Genetic disorders that masquerade as multiple sclerosis

There are many genetic disorders that have signs and symptoms suggestive of multiple sclerosis and that may easily be overlooked in the evaluation of both adult and pediatric multiple sclerosis patients. The recognition of a genetic disorder as the cause of a patient's "multiple sclerosis" phenotype has important implications not only for the patient, but often also for others in the patient's family who may be at risk for the same disease. We present here a review of single gene disorders that can masquerade as multiple sclerosis. For each disorder, the major clinical and biochemical characteristics are discussed, together with the appropriate testing to screen for and confirm the diagnosis. In addition, guidelines are presented for when to suspect an underlying genetic condition in a patient with a diagnosis of definite or probable multiple sclerosis. The great variety of genetic disorders that can masquerade as multiple sclerosis and the many implications of a genetic diagnosis underscore the importance of recognizing genocopies of multiple sclerosis.

Mendelian etiologies of stroke

There are many genetic disorders associated with an increased risk for stroke that may easily be overlooked in the evaluation of both adult and pediatric acute stroke victims. The recognition of a genetic disorder as the cause of a stroke has important implications not only for the immediate care of the stroke victim, but often also for others in the patient's family who may be at risk for the same disease and for whom preventive measures sometimes can be taken. We present here a comprehensive review of genetic disorders associated with stroke in the nongeriatric age groups for which a causative role in the evolution of stroke has been recognized or is likely. For each disorder, the major clinical and biochemical characteristics as well as the probable pathogenetic mechanisms of stroke are discussed, together with the appropriate testing required to screen for and confirm the diagnosis. The great variety of genetic disorders and mechanisms causing stroke underscores the increasing importance of understanding genetic disease for appropriate diagnosis and treatment of a common clinical problem affecting both children and adults.

Vascular malformations of the central nervous system: a morphological overview

Vascular malformations of the central nervous system (C.N.S.) are classified by size, location, and morphologic type, distinguishing capillary telangiectasias, cavernous malformations, venous angiomas, arteriovenous malformations (AVMs) including varix of the great vein of Galen, and other vascular malformations (e.g. Sturge-Weber syndrome). The morphology and predominant location pattern of the different types of vascular malformations in the brain and spinal cord, and their embryology are reviewed. In the brain and its coverings, all types mainly AVMs and venous angiomas do occur, representing 5-9% of all intracranial space-occupying lesions and 20-40% of the sources of surgically treated intracranial hemorrhages. 50-80% of the angiomas are located in the cerebral hemispheres, 10-18% in central brain areas (basal ganglia, internal capsule, choroid plexus), and 10-30% in the posterior fossa. The major types of cerebral vascular malformations are described with reference to their anatomical features, location, chief arterial and venous supply, and prominent complications. Spinal vascular malformations, accounting for 3 to 12% of spinal space-occupying lesions, include vertebral, extradural, dural, subpial and intramedullary angiomas which occur as isolated or complex vascular anomalies and may involve various covering layers at the same level. The preferential occurrence of angiomas on the dorsal surface of the cord and in the caudal regions is related to the embryologic development of spinal vasculature. Frequent association of spinal angiomas (20-25%) with other vascular anomalies and dysplasias emphasizes their hamartomatous nature and developmental origin. Spinal angiomas include capillary telangiectasias with extra- or intradural and, rarely, intramedullary location, cavernomas, mainly arising in vertebral bodies, venous angiomas, mainly located in vertebral bodies and in the extradural space, and AVMs constituting the commonest type, that may affect both the pial and radicular vessels and can penetrate into the cord. They present as simple AV fistulas, cirsoid angiomas with localized vascular plexuses and large complex convolutions ("juvenile" type). The complications of spinal angiomas include subarachnoid hemorrhage, rare epidural hematoma, hematomyelia, compression lesions of the cord and roots, and ischemic changes causing chronic progressive radiculomyelopathy, previously referred to as Foix-Alajouanine syndrome. Chronic damage to the cord and spinal roots results from pressure effects, thrombosis of the abnormal vessels, disorders of venous drainage, and "steal" phenomena related to the vascular anomalies.