How does hemangioblastoma (a type of benign tumor) cause syringomyelia (a condition characterized by the formation of a fluid-filled cavity within the spinal cord)?

Mechanism of Syringomyelia Formation in Hemangioblastoma

Hemangioblastomas cause syringomyelia primarily through obstruction of cerebrospinal fluid (CSF) flow and increased protein content in the CSF, leading to fluid accumulation within the spinal cord. 1

Pathophysiological Mechanisms

Hemangioblastomas are benign vascular tumors that can occur in the spinal cord and contribute to syringomyelia formation through several mechanisms:

1. CSF Flow Obstruction

• Hemangioblastomas typically develop on the surface of the spinal cord (subpial location), most frequently along its posterior aspect 2
• These tumors create a physical obstruction to normal CSF circulation between intracranial and spinal compartments 3
• The obstruction leads to altered CSF dynamics and pressure gradients within the spinal canal

2. Increased Protein Content

• Hemangioblastomas secrete vascular endothelial growth factor (VEGF) and other proteins
• These proteins increase the oncotic pressure within the CSF
• The altered oncotic pressure draws fluid into the central canal of the spinal cord

3. Vascular Factors

• Larger hemangioblastomas (>24mm) are invariably accompanied by vascular flow voids 2
• The abnormal vasculature associated with hemangioblastomas can disrupt normal blood flow to the spinal cord
• This vascular disruption contributes to syrinx formation through altered tissue perfusion

Clinical Correlation

The relationship between hemangioblastoma and syringomyelia is significant:

• Studies show that approximately 55% of patients with spinal hemangioblastomas develop syringomyelia 1
• Syringomyelia occurs more frequently when hemangioblastomas are located in the cervical segment compared to other spinal segments 1
• Symptomatic small hemangioblastomas typically have relatively large associated syringes, whereas asymptomatic ones do not 2

Anatomical Considerations

• Syringomyelia represents dilation of the central canal of the cord, analogous to hydrocephalus 3
• The syrinx can extend from the conus medullaris into the filum terminale 4
• Syringomyelia-induced disruption of sympathetic fibers in the thoracic spinal cord can lead to autonomic dysfunction, including syncope in rare cases 5

Clinical Implications

• Surgical removal of the hemangioblastoma and decompression of the spinal cord with opening of the syrinx is the treatment of choice 6
• After successful tumor removal, syringomyelia collapse or reduction typically occurs between two weeks and 15 months 1
• Improvement of spinal function is more significant in patients who experience syringomyelia reduction following surgery 1

Association with von Hippel-Lindau Disease

• Hemangioblastomas can occur sporadically or as part of von Hippel-Lindau (VHL) disease 5
• There is no significant difference in MR findings between sporadic and VHL-associated hemangioblastomas except for multiplicity and higher percentage of small tumors in VHL patients 2
• CNS hemangioblastomas occur in 60-80% of VHL patients, with spinal hemangioblastomas occurring in 13-50% 5

Early detection and treatment of hemangioblastomas are essential to prevent progressive neurological deficits from associated syringomyelia.