MRI semiotics and treatment of SDAVF
Diagnostic imaging of spinal dural arteriovenous fistula (SDAVF) and associated arteriovenous malformations (AVMs) is based on the identification of specific patterns. On T2-weighted tomograms, dilated veins (both intramedullary and perimedullary) appear as characteristic serpiginous areas of signal loss. This phenomenon is known as flow voids. These vascular structures show active contrast enhancement.
A direct consequence of the fistula's presence is pronounced venous congestion. On magnetic resonance tomograms, it manifests as edema: a poorly defined hyperintense signal on T2-WI, accompanied by spinal cord thickening. Additional signs of hemorrhage may be detected. The intensity of the MR signal in such areas varies and directly depends on the age (duration) of the extravasated blood. In some cases, the radiologist may detect concurrent subarachnoid hemorrhage or an intranidal aneurysm.
To achieve the most precise localization of the fistula (e.g., at the level of the L1 segmental artery) and visualize the ascending intradural vein, MR angiography (specifically the TWIST technique) and digital subtraction angiography (DSA) are used.
Treatment of arteriovenous malformations includes embolization. It may be radical (with therapeutic intent), but in practice, it is more commonly palliative and targeted. The goals of such intervention include eliminating pseudoaneurysms, reducing local venous hypertension, or preparing the vascular bed for open surgical treatment.
Spinal cord cavernous malformation (SCCM)
Spinal cord cavernous malformation (SCCM) has several synonyms: cavernoma, cavernous angioma, or cavernous hemangioma. Pathomorphologically, it is a vascular malformation consisting of closely apposed sinusoid-like vessels. A crucial diagnostic criterion is the complete absence of normal brain parenchyma between these vessels.
Cavernomas are significantly less common in the spinal cord than in the brain. Regarding localization, they may be extradural or intradural extramedullary, but the vast majority have an intramedullary location. Symptomatic SCCM cases require early surgical removal to prevent recurrence and recurrent hemorrhages.
The clinical presentation is divided into four main subtypes:
- Discrete episodes of neurological deterioration separated by asymptomatic intervals (ranging from hours to days) with varying degrees of recovery.
- Slowly progressive myelopathy.
- Acute neurological deficit with rapid clinical deterioration.
- Acute neurological deficit with gradual deterioration over weeks or months.
Clinical pathophysiology: episodes of acute deficit are hypothesized to be caused by recurrent microhemorrhages.
Cavernomas are occult (invisible) on conventional angiography, making MRI the primary imaging modality. Cavernomas exhibit a heterogeneous structure on T1-WI and T2-WI. The typical «popcorn» sign is formed by blood breakdown products of various ages. A rim of low signal intensity due to hemosiderin deposition is seen along the periphery on T2-WI. Gradient-echo sequences (GRE) reveal hypointense blooming artifact. Minimal contrast enhancement, edema, or spinal cord thickening is occasionally observed.
Spinal cord infarction
Spinal cord infarction is a rare pathology compared to cerebral infarction, which is explained by an abundant anastomotic blood supply network. Among established causes, aortic dissection and complications following aortic aneurysm repair are the most frequent, although the exact cause is often not identified. The thoracolumbar region is affected most commonly, and the cervical region less frequently. The territories of the anterior spinal artery (a. spinalis anterior) are typically involved.
Clinically, infarction is characterized by an acute onset: symptoms develop within minutes (unlike other myelopathies). The neurological deficit is frequently bilateral and accompanied by pain. When the a. spinalis anterior is affected, there is a classic loss of superficial pain and temperature sensitivity with relative sparing of tactile, vibratory, and proprioceptive sensation. Weakness and loss of all sensory modalities are strictly localized to the segmental level of the infarction.
MRI diagnostics:
- Acute phase: hyperintense signal on T2-WI in the ventral regions. On axial slices, the «owl's eyes» sign (owl's eyes) or «snake's eyes» sign (snake's eyes) is characteristic due to involvement of the anterior horns of the gray matter. Contrast enhancement is absent.
- Subacute phase: contrast agent enhancement appears.
- DWI: highly sensitive to acute ischemia. Restricted diffusion is detected as early as 30 minutes after symptom onset. This sequence is mandatory when infarction is suspected.
Spinal cord vasculitis
Spinal cord vasculitis is an inflammatory disorder of the vessel wall. The disease may be primary (idiopathic), also known as primary angiitis of the central nervous system, or secondary, developing in the setting of a wide range of other systemic diseases.
Briefly: answers to topical questions
Which systemic diseases most frequently cause secondary spinal cord vasculitis?
Sources indicate that spinal cord involvement in the context of immune-mediated and inflammatory disorders includes:
- Systemic lupus erythematosus (Systemic lupus erythematosus, SLE)
- Sjögren's syndrome
- Behcet's disease
Secondary CNS vasculitis may also be associated with infections, malignancies, and substance abuse.
What is the MRI semiotics of spinal cord vasculitis?
MRI findings of spinal cord involvement in vasculitis are nonspecific. Magnetic resonance tomograms visualize the following changes:
- Intramedullary lesions — long-segment or short-segment areas of hyperintense signal on T2-weighted images. On axial slices, they are frequently located dorsally and laterally, resembling multiple sclerosis plaques.
- Contrast enhancement — in the acute phase, lesions enhance following intravenous contrast administration.
- Leptomeningeal enhancement — meningeal contrast enhancement may be noted, particularly in the region of the cauda equina.
Which segments of the spinal cord are most frequently affected in spinal dural arteriovenous fistula?
In spinal dural arteriovenous fistula, the typical localization is the thoracolumbar region. SDAVFs are extremely rare in the cervical spine and are described only in the region of the foramen magnum.
MR angiography and digital subtraction angiography allow precise localization of the fistula. In SDAVF, elevated spinal venous pressure leads to slowed venous drainage, venous stasis, spinal cord edema, and ultimately ischemia.
Which arteries form the anastomotic blood supply network of the spinal cord, protecting it from infarctions?
The anastomotic blood supply network of the spinal cord is formed by longitudinal and segmental vessels creating multiple anastomoses in the proximal regions. The network is based on:
- Anterior spinal artery (a. spinalis anterior) and two posterior spinal arteries.
- Radicular branches (aa. radiculares) originating from segmental arteries.
Blood supply sources depend on the level:
- In the cervical region — the vertebral artery (a. vertebralis), as well as branches of the subclavian artery (thyrocervical and costocervical trunks).
- In the thoracic and lumbar regions, the thoracic and lumbar branches of the aorta (aorta). The dominant radicular artery here is the artery of Adamkiewicz (artery of Adamkiewicz).
Despite the rich network, peripheral intramedullary branches (e.g., the sulcocommissural artery) are end arteries, and their occlusion leads to infarction.
To remember the MRI appearance of a cavernoma, use the mnemonic: "Popcorn with a dark rim". The "popcorn" is a heterogeneous core of blood of varying ages (T1/T2-WI), and the "dark rim" is the hypointense hemosiderin rim on T2-WI.
Class and exam questions
Is a cavernous malformation visible on conventional angiography?
No, during angiography, cavernomas remain occult (invisible). The primary and most informative diagnostic method is MRI.
Does the spinal cord enhance with contrast in the acute phase of infarction?
In the acute phase of spinal cord infarction, contrast enhancement is absent. Enhancement in the ischemic zone appears only in the subacute period.
What is the purpose of targeted embolization in AVMs?
It is palliative in nature and used to exclude false aneurysms, reduce venous hypertension, or prepare tissues for surgery.
What else to study on this topic
- Topographic anatomy of the spinal cord blood supply and collateral pathways.
- TWIST MR angiography: physical principles and advantages in neuroradiology.
- Differential diagnosis of "owl's eye" and "snake's eye" signs in various myelopathies.
- Pathophysiology of the blooming artifact on GRE sequences.
- Clinical and radiological differences between primary and secondary CNS vasculitis.
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