Arteriovenous malformation (AVM)

The human spine is formed by individual vertebrae and connective tissue discs in between. The vertebrae form the spinal canal. There are seven cervical, twelve thoracic, and five lumbar vertebrae. The intervertebral discs are the link between the individual vertebral bodies.

The little joints that link the vertebrae together are known as facet joints. They help to stabilize the spine and, together with the intervertebral discs, allow a certain degree of mobility of the spinal cord. The spinal canal should be wide enough to allow nerve roots to float freely in cerebrospinal fluid. The front border of the spinal canal is built by the vertebral bodies and intervertebral discs, the side by the intervertebral joints (facets) and back by the ligamentum flavum (yellow band) and vertebral arches. Discs consist of an outer fibrous ring (annulus fibrosus), which surrounds an inner gel-like center (nucleus pulposus). The spinal cord and nerve roots lie within the spinal canal. The spinal cord extends downwards approx. to the 1st lumbar vertebra. Below, only nerve roots are present in the spinal canal. At the level of the intervertebral disc the nerve roots pass through the neural root foramina to exit the spinal canal. The spinal cord and nerve roots conduct electric-like signals from the skin and joints to the brain, and process of movement is initiated from the brain to the muscles.

An arteriovenous malformation (AVM) is an abnormal connection of arteries and veins, which disrupts normal blood flow and oxygen circulation. Spinal vascular lesions comprise approximately 4 % of all intradural spinal lesions. Early recognition is mandatory to halt the progression of the disease and minimize permanent spinal cord injury (PMID: 27075861). The clinical presentation of spinal AVMs can be acute (associated with a hemorrhage) or a protracted course (secondary to venous congestion, spinal cord ischemia, or mass effect). ABF classification of spinal vascular malformations: Type I - Spinal dural arteriovenous fistula (AVF): located at the dural sleeve of a spinal root, associated with a single-coiled vessel on the dorsal pial surface of the spinal cord Type II - Glomus AVM (intradural. high flow): true intramedullary nidus and with the arteriovenous shunting occurring deep into the pia mater Type III - Juvenile AVM (intradural. high flow): involvement of one or more metameres (and consequently of portions of the neural tissue, dura, bone, muscle and/or skin) Type IV - Direct/perimedullary AVF (intradural. high flow): usually supplied by the anterior spinal artery, and drainage through the pial venous network, leading to an aneurysmal dilation of the draining veins (PMID: PMID:888091).

Hemorrhage within the spinal cord or the spinal canal

Chronic damage to the spinal cord due to venous hypertension, ischemia, or mass effect

Total/partial paralysis and numbness from the site of the spinal cord damage downwoads

Unsteady gait (especially in dark rooms) Stiffness, numbness and weakness of the hands and legs Retention, or unintended urinary incontinence Numbness of the genitals and loss of sexual function

Conus medullaris AVMs may cause radiculopathy and myelopathy at the same time

Neurological symptoms caused by the arteriovenous malformation

To halt or reverse the progressive neurological deterioration by restoring normal spinal cord perfusion and intravascular pressures.

Surgical resection

Endovascular embolisation

Type I - surgical obliteration or endovascular treatment. Open surgery is relatively safe and highly effective procedure with a reported success rate of above 90% (PMID: 22537120). Motor function improved in 82.2% patients and symptoms were stabilized in 14.4% patients (PMID: 20871454). The sucess rate of the endovascular treatment ranges between 70%–90% with a Recurrence rate up to 20% (PMID: 19408993). Type II - First-line treatment is endovascular embolization. Surgical treatment aiming to remove the nidus has a significant risk for causing neurological damage (PMID: 19442003). Type III - Both endovascular embolisation and surgical obliteration are possible. Optimal treatment strategy remains to be established (PMID: 26948701). Type IV - In most cases a combined treatment (endovascular and surgical) is required (PMID: 26948701).