Hemodynamic Patterns of Spinal Cord Perfusion in Thoracoabdominal Aortic Aneurysm Repair

Paraplegia in aortic surgery is due to its impact on spinal cord perfusion whose hemodynamic patterns (SCPHP) are not clearly defined. Detailed morphological analysis of vascular network and collateral network modifications within Monro–Kellie postulate due to the fixed theca confines was performed to identify SCPHP. SCPHP may begin with intraspinal “backflow” (I-BF), that is, hemorrhage from anterior and posterior spinal arteries, backward via the connected anterior and posterior radicular medullary arteries, through the increasing diameter and decreasing resistance of segmental arteries (SAs), off their aortic orifices outside vascular network at 0 operative field pressure. The I-BF blood bypasses both intra- and extraspinal capillary networks and causes depressurization (0 diastolic pressure) and full ischemia of dependent spinal cord. When the occlusion of those SAs orifices arrests I-BF, the hemodynamic pattern of intraspinal “steal” (I-S) may take place. The formerly I-BF blood, in fact, is now variably shared between the fraction maintained in its physiological intraspinal network and that keeping flowing as I-S through the extraspinal capillary network. I-S is, however, counteracted by the extraspinal “steal” from the connected mammary/paraspinous-independent extraspinal feeders, all physically competing for the same room left by the missed physiological SA direct aortic blood inflow. Steal phenomenon evolves within the 120-hour time frame of CNm, whose intraspinal anatomical changes may offer the physical basis within the Monro–Kelly postulate, respectively of the intraoperative and postoperative paraplegia. The current procedures could not prevent the unphysiological SCPHP but awareness of details of their various features may offer the basis for improvements tailored, to the adopted intra- and postoperative procedures.

MORPHOLOGY AND MORPHOMETRIC ANALYSIS OF FORAMEN MAGNUM IN ADULT HUMAN SKULLS

Background: The Foramen magnum is an important landmark present at the base of the skull, it serves as a transitional zone between spine and skull. It is closely related to vital structures such as medulla oblongata, meninges, anterior and posterior spinal arteries, vertebral arteries and spinal accessory nerve, passing through it hence thorough knowledge of foramen magnum is required. These structures passing may undergo compression in case of foramen magnum herniation, meningiomas and foramen magnum achondroplasia. Aims: The present study aims in performing the morphometric analysis foramen magnum and to classify it based on its shape. Materials and methodology A total number of 64 adult dry human skulls were evaluated from the Department of Anatomy, ESIC MC & PGIMSR, Rajajinagar, Bengaluru, Karnataka. Results: The mean antero-posterior diameter was found to be 34.10 ± 2.63 mm, mean transverse diameter was 28.07 ± 1.87 mm, with mean area of 752.07 ± 111.97 mm2 and foramen magnum index was 1.21 ± 0.12. The foramen magnum shapes were classified as oval (30%), circle (12%), hexagonal (3%), pentagonal (5%), egg (17%), leaf (6%), irregular (27%). Conclusion: The morphometry along with other parameters can be used for sex determination in partially damaged skull bones of unknown individuals. The obtained data is useful not only for anatomists but also the neurosurgeons, otorhinolaryngologist and radiologists. Keywords: Foramen Magnum, Morphometry, Meningioma, Achondroplasia, Antero-Posterior Diameter, Transverse Diameter, Foramen Magnum Area, Foramen Magnum Index.

ANATOMY OF THE SPINAL CORD’S BLOOD SUPPLY. Review

Relevance. The traditional scheme of blood supply to the spinal cord, formed in the 60-70s of the last century, does not correspond to the pathogenesis of many neurological disorders of the spinal cord. There is also a discrepancy in terminology: the names of arteries found in surgical and neurological works do not correspond to the names of the International Anatomical Nomenclature. Therefore, today this issue needs further analysis. Objective: to summarize the information of different authors on the number of spinal branches and their branches, topography, blood supply to each segment of the spinal cord, to analyze the individual variability of sources of blood supply to the spinal cord. Materials and methods. Analysis of scientific publications in the international electronic scientometric database PubMed by keywords for the period 2000-2018. and comparing these data with the imaginations of 1760-1993. Results. The idea of ​​the structural organization of the blood supply to the spinal cord has changed. With modern data, intracranial sources, namely: anterior and posterior spinal arteries, the blood supply to the true cervical spinal cord, and the rest of the department - lower cervical, thoracic, lumbar, sacral and coccygeal - blood supply from extracranial sources, and they exist in this area segmental branches of the aorta. Nowadays, extracranial sources are considered the main in the blood supply to the spinal cord. It is now known that the anterior and posterior spinal arteries are intermittent and cannot provide blood supply to the spinal cord, as previously thought. The general plan of arterial blood supply of a spinal cord can be presented in the form of a set of pools of front and back radical (radiculomedullary) arteries. The anterior radicular arteries are 4-8, and the posterior 15-20, respectively, along the spinal cord in its ventral and dorsal departments the same number of arterial pools are formed. There are anastomotic connections between these pools, which are not always functionally complete. Each of these basins is supplied by a separate radiculomedullary artery. Each such artery feeds not one but several segments of the spinal cord. The number and levels of approach to the spinal cord of radiculomedullary arteries, especially the anterior ones, differ significantly in individual variability. The perception of the vascularization of the cervical spinal cord was analyzed. At different times, information about the number of arteries that supplied blood to this department differed significantly: in 1760 it was believed that it was 31 arteries; and in 1882-1939 - only 7; in 1943 - 27, in 1958 - 6-8; in 1958 - 7-10; in 1961-1963 - 5-8; in 1966-1973 - 5; in 1993 - 1-2 arteries. Such different information about spinal cord vascularization is the result of significant individual variability. Conclusions. Incomplete current knowledge about the blood supply to the spinal cord is the cause of unresolved problems of etiology, pathogenesis, and clinical course of spinal ischemic strokes, including cervical localization. The existing terminological confusion regarding the names of the arteries that supply blood to the spinal cord, in particular its cervical region, is explained by the significant variability of the radiculomedullary arteries of this zone in terms of number, diameter, and location. Due to the existence of arterio-venous anastomoses, arterial myelobulbar anastomoses, adjacent areas of blood supply in this area, theft phenomena are formed and distant foci of ischemia appear, including both the spinal cord and the brain. Therefore, in order to make an angiotopic diagnosis, it is necessary to take into account not only anatomical but also physiological and pathophysiological aspects of regulation and compensation of cerebral circulation.

Ruptured Conus Medullaris Arteriovenous Malformation

Conus medullaris arteriovenous malformations are an exceedingly rare cause of neurological deficit. They occupy the tip of the spinal cord and can generate motor, sensorty, bowel, bladder, or sexual function deficits. Because of the complex vascular supply of the caudal aspect of the spinal cord, which usually includes multiple feeders from both the anterior and posterior spinal arteries, management may be endovascular, microsurgical, or both. Making the proper diagnosis and distinguishing it from other similar pathologies such as arteriovenous fistula is critical. As with other spinal arteriovenous malformations, it is usually not necessary to pursue the nidus into the spinal cord parenchyma at the time of surgery. This chapter discusses the diagnosis and management of this rare disorder.

Spinal Cord Infarction

This chapter discusses spinal cord infarctions, which are rare but with devastating consequences. It is associated with surgical procedures that compromise oxygen supply to the spinal cord, arteriosclerosis, embolism of the spinal cord circulation, or compression of blood vessels of the spinal cord. The most common of spinal neurovascular syndromes is the anterior spinal artery syndrome, caused by infarction in the anterior two-thirds of the cord. This syndrome spares the dorsal columns as the posterior one-third of the spinal cord is supplied by a pair of posterior spinal arteries. It is characterized by complete motor paralysis below the level of the lesion; loss of pain and temperature sensation with sparing of proprioception and vibratory sensation; and autonomic dysfunction, such as hypotension, sexual, and bowel and bladder dysfunction. MRI imaging, biochemical and immunological studies from cerebrospinal fluid and blood, and spinal angiography can be considered to confirm the diagnosis and delineate the cause. Treatments are directed at managing motor paralysis and spasticity, sensory dysfunction and pain, and autonomic dysfunction that includes neurogenic bladder and autonomic dysreflexia. Cervical and thoracic spinal cord injury affects respiratory muscles, causing pneumonia, in addition to autonomic dysreflexia. Preventive measures during abdominal aorta aneurysm surgery include neuromonitoring of the spinal cord, spinal fluid drainage, induced hypothermia, and use of pharmacological adjuncts such as intrathecal papaverine. Precautions in using particulate steroids for transforaminal epidural injection in pain management may help reduce the risk of articular embolism in the spinal cord or brainstem.

Microsurgical Treatment of Recurrent Conus Medullaris Arteriovenous Malformation: 2-Dimensional Operative Video

Arteriovenous malformations (AVMs) involving the conus medullaris have a unique angioarchitecture due to their involvement of the arterial basket of the conus medullaris, which represents an arterial anastomotic network between the anterior spinal artery (ASA) and posterior spinal arteries (PSAs) at the level of the conus medullaris.1 These lesions consist of a combination of a true AVM nidus, which is usually extramedullary, and direct shunts between the ASA, PSAs, and the venous system. Patients may present with radiculopathy, myelopathy, or subarachnoid hemorrhage.2 A 40-yr-old woman status post T11-L1 laminoplasty for resection of a ruptured conus AVM 6 yr prior presented with routine follow-up angiography suggestive of an arteriovenous fistula. She was counseled regarding treatment options including endovascular embolization and microsurgical ligation or resection, and she elected to proceed with surgical treatment. At the time of surgery, a recurrent AVM was noted. A 2-dimensional intraoperative video illustrates the microsurgical treatment of her recurrent conus AVM. The patient recovered well postoperatively. Spinal angiography demonstrated complete obliteration of the lesion. The patient experienced transient urinary retention that was self-limited but otherwise was without any new neurological deficit. Due to the retrospective nature of this report, informed consent was not required. Video used with permission from Barrow Neurological Institute, all rights reserved.

Microsurgical anatomy of the arterial basket of the conus medullaris

OBJECT The arterial basket of the conus medullaris (ABCM) consists of 1 or 2 arteries arising from the anterior spinal artery (ASA) and circumferentially connecting the ASA and the posterior spinal arteries (PSAs). The arterial basket can be involved in arteriovenous fistulas and arteriovenous malformations of the conus. In this article, the authors describe the microsurgical anatomy of the ABCM with emphasis on its morphometric parameters and important role in the intrinsic blood supply of the conus medullaris. METHODS The authors performed microsurgical dissections on 16 formalin-fixed human spinal cords harvested within 24 hours of death. The course, diameter, and branching angles of the arteries comprising the ABCM were then identified and measured. In addition, histological sections were obtained to identify perforating vessels arising from the ABCM. RESULTS The ASA tapers as it nears the conus medullaris (mean preconus diameter 0.7 ± 0.12 mm vs mean conus diameter 0.38 ± 0.08 mm). The ASA forms an anastomotic basket with the posterior spinal artery (PSA) via anastomotic branches. In most of the specimens (n= 13, 81.3%), bilateral arteries formed connections between the ASA and PSA. However, in the remaining specimens (n= 3, 18.7%), a unilateral right-sided anastomotic artery was identified. The mean diameter of the right ABCM branch was 0.49 ± 0.13 mm, and the mean diameter of the left branch was 0.53 ± 0.14 mm. The mean branching angles of the arteries forming the anastomotic basket were 95.9° ± 36.6° and 90° ± 34.3° for the right- and left-sided arteries, respectively. In cases of bilateral arterial anastomoses between the ASA and PSA, the mean distance between the origins of the arteries was 4.5 ± 3.3 mm. Histological analysis revealed numerous perforating vessels supplying tissue of the conus medullaris. CONCLUSIONS The ABCM is a critical anastomotic connection between the ASA and PSA, which play an important role in the intrinsic blood supply of the conus medullaris. The ABCM provides an important compensatory function in the blood supply of the spinal cord. Its involvement in conus medullaris vascular malformations makes it a critical anatomical structure.

High cervical arteriovenous fistulas fed by dural and spinal arteries and draining into a single medullary vein

Object The authors previously reported a case of complex arteriovenous fistula (AVF) at C-1 with multiple dural and spinal feeders that were linked with a common medullary venous channel. The purpose of the present study was to collect similar cases and analyze their angioarchitecture to gain a better understanding of this malformation. Methods Three such cases, affecting 2 males and 1 female in their 60s who had presented with hematomyelia (2) or progressive myelopathy (1), were treated surgically, and the operative findings from all 3 cases were compared using digital subtraction angiography (DSA) to determine the angioarchitecture. Results The C-1 and C-2 radicular arteries and anterior and posterior spinal arteries supplied feeders to a single medullary draining vein in various combinations and via various routes. The drainage veins ran along the affected ventral nerve roots and lay ventral to the spinal cord. The sites of shunting to the vein were multiple: dural, along the ventral nerve root in the subarachnoid space, and on the spinal cord, showing a vascular structure typical of dural AVF, that is, a direct arteriovenous shunt near the spinal root sleeve fed by one or more dural arteries and ending in a single draining vein, except for intradural shunts fed by feeders from the spinal arteries. In 2 cases with hemorrhagic onset the drainer flowed rostrally, and in 1 case associated with congestive myelopathy the drainer flowed both rostrally and caudally. Preoperative determination of the shunt sites and feeding arteries was difficult because of complex recruitment of the feeders and multiple shunt sites. The angioarchitecture in these cases was clarified postoperatively by meticulous comparison of the DSA images and operative video. Direct surgical intervention led to a favorable outcome in all 3 cases. Conclusions A high cervical complex AVF has unique angioarchitectural characteristics different from those seen in the other spinal regions.