Complications of Surgery for Intrinsic Spinal Cord Tumors

Highlights

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Intramedullary spinal cord tumors are rare and challenging entities, comprising 16% to 58% of all primary spinal cord and 2% to 8.5% of all primary central nervous system tumors in the adult and pediatric populations.
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Common complications encountered with spinal cord tumor surgery include intraoperative damage to spinal cord tracts leading to motor and sensory deficits, and cerebrospinal fluid leak.
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When approaching the lower thoracic spinal cord levels, the surgeon should investigate the location of the artery of Adamkiewicz.
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Complications can be avoided by use of intraoperative monitoring, neuronavigation, and careful examination of patient imaging.

Introduction

Intramedullary spinal cord (IMSC) tumors are rare and challenging entities, comprising 16% to 58% of all primary spinal cord and 2% to 8.5% of all primary central nervous system tumors in the adult and pediatric population. The ependymoma, astrocytoma, and hemangioblastoma correspond to more than 90% of all IMSC tumors. Other IMSC tumors such as glioma, cavernoma, hamartoma, metastases, inclusion tumor, cyst, neurocytoma, melanocytoma, and lipoma are rarely encountered. Several genetic factors have been associated with IMSC tumors. Neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and von Hippel-Lindau disease (VHL) are the most common genetic diseases that are prone to cause the development of astrocytoma, ependymoma, and hemangioblastoma, respectively. Approximately 20% of patients affected by NF1 and NF2 will develop an IMSC tumor. 15% to 25% of hemangioblastomas are associated with VHL syndrome, an autosomal dominant condition with incomplete penetrance and incomplete expression.

IMSC tumors are particularly related to syringomyelia (25%–58%), especially those tumors located in the lower cervical and upper thoracic spine. The occurrence of a syrinx is seen as a sign of a favorable outcome after resection because it denotes a noninfiltrative tumor and a rapid postoperative recovery after the resolution of the fluid-filled cavity. Half of the syringes occur above the tumor, whereas 40% are above and below, and only 10% are primarily below the tumor.

Anatomic Insights

The spinal cord (SC) has a cylindrical shape that is slightly flattened in the anteroposterior axis. It follows the curvature of the vertebral column and shows two characteristic enlargements, namely the cervical and lumbar ones, where motor neurons related to the upper and lower limbs concentrate. The conus medullaris is aligned to the first lumbar vertebra and gives rise to more than 50 rootlets over a length of <3 cm. The SC is covered by the flexible vertebral column and the meninges. At the spinal level, the dura is arranged in three layers, contrary to the two-layer intracranial dura. The internal layer is in continuity with the inner dural layer of the head, the middle layer is connected to the external dural layer of the head, and the external layer continues as the periosteum of the skull. Under and loosely attached to the dura is the arachnoid layer, which contains the subarachnoid space filled with cerebrospinal fluid (CSF). It also extends to the dural sac. The arachnoid covers the spinal nerves toward the root sleeves, where it fuses with the dura. Within the subarachnoid space, several septations have been described, especially in the posterior space, where there is a longitudinal dorsal or dorsolateral septum from the arachnoid to the spinal pial surface dividing the subarachnoid space into left and right halves. The pia mater is the innermost meningeal layer and encases the spinal cord. It provides a barrier between the subarachnoid space and the perivascular spaces. The pia is firmly attached to the dura by 21 pairs of extensions, called the denticulate ligaments. They run alongside the spinal cord to the level of the conus medullaris, where they end between the last thoracic and the first lumbar nerves. In the center of the SC lies the central canal. It consists of the remnants of the neural tube central cavity lined by ependymal cells and filled with CSF. The anterior and posterior commissures enclose the central canal. The gray matter horns are somatotopically organized and contain different classes of functional neurons. As a result, motor neurons that innervate axial muscles are medially located in the ventral horn, whereas motor neurons that control distal limb movements are located more laterally. Finally, motor neurons responsible for controlling proximal limb muscles lie in between. The posterior horn has a layered neuronal organization that is based on synaptic inputs and outputs. The superficial layers receive exteroceptive sensory information about pain, temperature, and light touch, and generate the contralateral spinothalamic tracts. The deep layers are involved with proprioceptive information and contribute to the ipsilateral spinocerebellar tracts. The posterior cervical horn also includes the spinal nucleus of the trigeminal nerve. The white matter is organized in tracts associated with major motor or sensory functions. The posterior column enlarges, as the SC ascends, to include more axons carrying fine-touch, vibration, and proprioceptive information from the lower limbs medially (fasciculus gracilis) and the upper limbs laterally (fasciculus cuneatus). The lateral column contains the two most prominent ascending tracts, namely the lateral spinothalamic and the spinocerebellar ones, and one descending tract, the lateral corticospinal tract. Finally, the anterior spinothalamic and corticospinal tracts are found in the anterior column. The spinal vascular anatomy starts in the segmental extraspinal arteries, which correspond to the pathways of blood from the aorta and provide the arterial supply to not only the cord, but also to the nerve roots, dura, and paraspinal musculature. Each segmental artery has a ventral and a dorsal branch. The dorsal division gives off a spinal branch, which splits into the retrocorporeal (anterior spinal canal), prelaminar (posterior spinal canal), and radicular arteries. The radicular artery is termed the radiculomeningeal artery when it feeds the nerve roots and dura at every level. On the other hand, if these arteries take part in the cord vascular network, they are better termed radiculomedullary arteries if they supply the anterior spinal artery (ASA), and radiculopial or posterior radiculomedullary arteries if they supply the posterior spinal arteries (PSAs) and surface vasocorona of the SC. The artery of Adamkiewicz is also known as the great radicular artery or even as arteria radiculomedullaris magna and has a left-sided predominance. As the artery pierces the dura, a slight caudal turn may occasionally be seen. The artery then joins the ventral root on its way to the ventral surface of the SC, where the artery anastomoses with the ASA at or just before its typical and characteristic hairpin turn. The PSAs receive approximately 10 to 28 feeders, which can also demonstrate a hairpin configuration in the paramedian locations.

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