John Ratliff, MD and Edward Connolly, MD
Department of Neurosurgery; Louisiana State University Medical Center and
Ochsner Clinic
New Orleans, Louisiana
[Introduction | Case Presentation | Discussion | Type I AVM | Type II AVM | Type III AVM | Type IV AVM | References]
Introduction:
Vascular malformations of the spinal cord and dura compose 3-4% of spinal
cord masses. While these tumors are rare, they remain important clinical
entities and may yield severe neurological deficits and even death if not
recognized and treated appropriately. Due to their rare nature, these lesions
are not often considered in the differential diagnosis of patients presenting
with spinal cord masses or progressive myelopathy. At the Ochsner Medical
Foundation, two patients recently presented with the most common variety
of spinal arteriovenous malformation (AVM), the dural arteriovenous fistula.
In this article, we will briefly present the clinical history and evaluation
of one of these patients, and then review the different types of spinal
AVMs. Spinal arteriovenous malformation should be included in the differential
diagnosis of any patient presenting with progressive myelopathy and a cord
mass recognized on imaging studies.
Case Presentation:
TW is a 66 year old right handed white male who presented with a 6 months
history of progressive lower extremity weakness. By the time of neurosurgical
evaluation, the patient required assistance of a cane or walker for ambulation.
The weakness was symmetric, with both proximal and distal musculature affected
equally. TW also noted bilateral lower extremity "tingling," most
notable over the hips and anterior thighs, with onset approximately 3 months
prior to presentation. There was no significant associated pain. There was
no history of either cranial or spinal trauma. The patient noted no bowel
or bladder difficulty.
Examination revealed diminished motor strength (4- to 4+/5) bilaterally, with proximal musculature affected more than distal group. The patient reported diffuse decrease in sensitivity to pin prick and light touch, although no dermatomal distribution to the sensory loss was evident. There was no sensory level. Proprioception and vibratory sense were impaired in both lower extremities. Deep tendon reflexes were hyperactive (3/4) in both lower extremities. Babinski reflexes were present bilaterally. No clonus was evident. The patient's gait was grossly spastic, and a walker was required for ambulation. No fasiculations or fibrillations were evident. There was no gross muscular atrophy. Rectal exam was heme negative with good tone. The remainder of the neurological exam revealed no abnormalities.
The patient was evaluated initially with MRI
of the cervical, thoracic, and lumbar spine. The only abnormality seen
in this exam was increased signal
on T2 weighted images within the thoracic cord, extending from approximately
T-4 to T-12. The cord was noted to be slightly enlarged over this region,
with very mild to no contrast enhancement- see Figure 1. No
other pathology was evidenced. Differential diagnosis of this lesion
included
focal demyelination, post-infectious or post-inflammatory myelitis,
cord ischemia or infarction, sarcoidosis, and primary or metastatic
neoplasm.
Repeat MRI 2 months later revealed only a slight increase cord diameter
from T-6 to T-8; there was no contrast enhancement.
Due to the inconclusive MRI findings, thoracic myelography and post-myelogram CT were obtained. Vascular dilatation was evidenced posteriorly within the thecal sac on both exams, although on plain myelogram the lesion was most evident (Figure 2).
Thoracic spinal angiography revealed a spinal dural arteriovenous fistula at T-10 with prominent superior venous dilatation (Figure 3).
Due to the large size of the feeding radicular artery and fear of cord infarction with interventional radiologic occlusion of the lesion, the patient was taken to the OR for ablation of the fistula. Venous dilatation was marked at the time of exploration (Figure 4A), and a single feeding vessel was located at the site of dural nerve root entry (Figure 4B).
The patient tolerated the procedure without difficulty, and is now undergoing
physical therapy for rehabilitation of persistent lower extremity weakness.
Discussion:
This case illustrates some of the diagnostic difficulties encountered in
evaluation of spinal vascular pathology, and also evidences the delay in
diagnosis which often complicates these lesions. We will now review the
four different types of spinal AVM's, note their different epidemiologic
and clinical aspects, and cover different treatment options. Readers interested
in a more thorough review of endovascular therapy in spinal AVM's are referred
to a recent review by Hodes et al (see references below).
Type 1 Spinal AVM: Dural Arteriovenous
Fistula
Dural arteriovenous fistulas are the most common variety of spinal cord
AVMs, comprising 80-85% of spinal AVMs. These lesions show a male predominance
(80-90%) and generally present in late adulthood, ages 40-60. Presentation
is generally with radiculomyelopathy, followed by slow but progressive neurological
deterioration. Subarachnoid hemorrhage is very uncommon in dural AV fistulas,
and acute deterioration in neurologic function is unlikely.
Site of pathology in these lesions is within the dural root sleeve, where a direct arteriovenous fistula develops, generally with a single dural artery feeder vessel (Figure 4 above). Additional small feeding vessels from adjacent levels may also penetrate the dural and contribute to venous outflow. Hence these lesions are not true AVMs but instead AV fistulas. Venous drainage of the AV fistula is by a high-pressure, low-flow arterialized vein intradurally. Venous dilatation may extend rostrally and caudally from the fistula site. Eventual drainage is to the coronal venous plexus. Increased pressure in the coronal venous plexus yields spinal cord dysfunction, via chronic venous hypertension and loss of autoregulatory tone. Increased venous pressure yields chronic spinal cord ischemia, cell loss, and cord atrophy. Impaired autoregulation yields direct transmission of changes in systemic arterial pressure to the spinal cord without the normal dampening effect of the venous plexus.
Goal of treatment is isolation and obliteration of the fistula
and draining veins, which normalizes venous pressure and corrects venous
hypertension.
Two different therapeutic modalities are possible: embolization of
the feeding vessel, via endovascular techniques, and direct surgical
ligation, through
laminectomy and direct intradural exposure of the fistula. Fistula
obliteration yields correction of the lesion; resection of arterialized
veins is not
necessary and may actually be traumatic to the spinal cord. Embolization
in well chosen cases is a safe and effective therapy for dural AV fistulas.
In cases where the site of origin of the AV fistula is a large radicular
artery and embolization may be difficult or dangerous, direct surgical
exposure is preferred.
Type II Spinal AVM: Intramedullary
AVM
This is a true intramedullary arteriovenous malformation of the
spinal cord. These lesions are characterized by a compact intramedullary
nidus,
with feeding vessels arising from the anterior or posterior spinal
arteries, or both, and drainage into an arterialized coronal venous
plexus. Figure
5 depicts a type II spinal AVM with an intramedullary nidus. In
contradistinction to spinal AV fistulas, flow within these lesions
is high pressure and low
flow, with rapid filling on angiogram and early venous drainage.
Intramedullary AVMs have equal incidence distribution between men and women, and generally present at a much earlier age (average age of presentation: 24). The clinical course of these lesions is marked by progressive and fluctuating myelopathy, often overlaid by periods of acute neurologic deterioration secondary to hemorrhage within the AVM. Sudden apoplectic presentation, often with profound neurologic impairment and possible transverse myelopathy, is common in spinal AVMs. SAH often occurs in these lesions, occurring in 50% of cases. While dural AV fistulas are more commonly found in the lower thoracic and lumbar spine, true intramedullary AVMs occur throughout the cord, and hence presentation with upper extremity symptoms is possible.
Treatment of intramedullary spinal AVMs involves initial embolization
of feeding vessels using particulate matter. Immediate clinical improvement
is often noted after embolization, through reduction in arterial steal
and
improved cord perfusion; however, recanalization may occur over time,
with continued risk of hemorrhage. Hence, surgical resection of residual
nidus
after embolization is generally considered.
Type III Spinal AVM: Juvenile AVM
Juvenile spinal AVMs are extremely rare lesions. These lesions
are again true AVMs, with an intramedullary nidus which may occupy
the entire spinal
canal at the involved level. Cord tissue is present within the AVM
interspaces. Extramedullary and even extraspinal extension of the lesion
is possible
(Figure 6).
Juvenile AVMs are large and complex lesions, with multiple arterial feeding
vessels often arising from different cord levels. Hemodynamically, this
lesion manifests both high flow and high pressure, often yielding an auscultatable
spinal bruit over involved levels. They occur most commonly in adolescents
and young adults. Presentation and treatment are similar to type II AVMs;
however, prognosis for these lesions, considering their size and vascular
complexity, is understandably very poor.
Type IV Spinal AVM: Perimedullary Arteriovenous
Fistula
These rare lesions are similar to type I spinal AVMs, in that they are
not true AVMs but instead arteriovenous fistulas. The fistulous connection
in this lesion is intradural but extramedullary, with feeding vessel or
vessels arising from the anterior spinal artery. Venous drainage is via
an enlarged coronal venous plexus. No small vessel network or glomus is
evident connecting arterial and venous halves of the circuit (Figure
7). These lesions were first described by Djindjian, and then classified
as a type IV spinal AVMs by Heros et al.
These lesions may present in young adults, but presentation in the third
to sixth decade is more likely. SAH is possible with intradural AV fistulas,
with subsequent acute neurologic deterioration. A gradual but progressive
neurologic deterioration is common.
Three subcategories of intradural spinal AV fistulas have been recognized,
with different treatment options appropriate for each. The simplest of these,
the type IVa, features a single feeding vessel, often the artery of Adamkiewicz,
with low flow through the arteriovenous shunt and moderate venous enlargement.
Endovascular techniques are difficult with these lesions, due to the small
size of feeding vessels. Surgical excision is therefore often mandated.
Type IVb AV fistulas are intermediate in size, often with multiple feeding
vessels, and more marked venous enlargement. Venous ectasia may develop
at the site of shunting. Embolization in these lesions is easier, due to
the increased size of feeding vessels. In cases of incomplete shunt obliteration
with an endovascular approach, direct surgical excision may be necessary.
The largest of the intradural AV fistulas are the type IVc, which feature
giant, multipediculated fistulas, high blood flow, and large, tortous draining
veins. Spinal ischemia may develop in these lesions secondary to vascular
steal. Due to the size of these lesions, surgery is technically difficult
and may jeopardize the spinal cord. Treatment is hence through combination
of endovascular ablation, followed by surgical excision of retained elements.
References: