Cognard Type V Dural Arteriovenous Fistula
Cognard classification Type V of Dural Arteriovenous Fistula (dAVF), is a rare subtype of cranial dAVF, characterized by congestion of the perimedullary venous system with drainage into a spinal vein. Dysfunction of the medulla and spinal cord caused by venous hypertension is the most probable cause of the neurological symptoms in such cases 1).
Frequently located around the foramen magnum most commonly fed by dural branches of the vertebral artery and external carotid artery. Detection requires meticulous angiography to define the angioarchitecture of the fistula, which in turn defines the treatment modality.
Roelz et al., suggested performing contrast-enhanced MR angiography or even digital subtraction angiography in the presence of an unclear edematous brainstem lesion before scheduling stereotactic biopsy 2).
Anterior venous drainage is dominant. Because the anterior spinal veins are located subpially, flow voids are less prominent on sagittal T2-weighted MRI. This may lead to difficulties in diagnosing. Evaluation with MR angiography may compensate for these limitations 3).
Because of this typical features aggressive treatments should be considered.
The optimal approach for each case should involve discussions among a multidisciplinary team of interventional neuroradiologists, neurosurgeons, neurologists, and radiation oncologists. Careful assessment of a patient’s clinical presentation, current status (age, medical condition, comorbidities), and type of lesion (location, classification, and angiographic features) should be conducted before embarking on any treatment 5).
To eliminate venous congestion of the spinal cord, various approaches including surgical interruption of the spinal draining vein or transarterial embolization with cyanoacrylate have been reported. The introduction of nonadhesive Onyx has changed the treatment of dAVF, although little is known about the clinical usefulness of this type of fistula 6).
The endovascular technique is the gold standard treatment in dural arteriovenous fistulas. Due to the limited number of series published it is difficult to create rigid guidelines in terms of the best endovascular treatment approach. Treatment must be tailored to each particular case, but it is important to keep in mind that the possibility of treating a type V dAVF by the transvenous approach should not be discarded. In selected cases the transvenous approach may be helpful to increase the chance of success in the endovascular treatment of type V dAVF 7).
Sattur et al., presented the case of a 63 yr old woman, with prolonged, severe and progressive lower extremity myelopathy for 6 yr, with T2-weighted signal changes in the thoracic spinal cord on magnetic resonance imaging (MRI). Cervical MRI was unremarkable. Following computed tomography (CT), angiography of the spinal canal that revealed tortuous and dilated veins on the thoracic spinal cord surface, catheter angiography was performed. This demonstrated a fistula in relation to a dural branch of left vertebral artery with a characteristic single draining vein coursing caudally to the thoracic level, with delayed outflow suggestive of venous hypertension. Given the fact that the dural feeder was tortuous and relatively small, thus, precluding distal microcatheter access, and with presence of a single accessible draining vein, microsurgical treatment was preferred. Following a midline suboccipital craniotomy in prone position, a limited vertical dural opening was performed. Careful microsurgical arachnoid dissection revealed the arterialized draining vein with the aid of Indocyanine green videoangiography. The draining vein was clipped, coagulated, and disconnected. Postoperative recovery was uneventful and the patient is undergoing rehabilitation therapy. Follow-up angiographyshowed complete elimination of the fistula 8).
Jermakowicz et al., published the first known case of a pediatric. A 14-year-old girl presented with a 3-week history of slowly progressive unilateral leg weakness that quickly progressed to bilateral leg paralysis, sphincter dysfunction, and complete sensory loss the day of her presentation. MRI revealed an extensive T2 signal change in the cervical spine and tortuous perimedullary veins along the entire length of the cord. An emergency cranial angiogram showed a Type V dAVF fed by the posterior meningeal artery with drainage into the perimedullary veins of the cervical spine. The fistula was not amenable to embolization because vascular access was difficult; therefore, the patient underwent urgent suboccipital craniotomy and ligation of the arterialized venous drainage from the fistula. The patient’s clinical course immediately reversed; she had a complete recovery over the course of a year, and she remains asymptomatic at the 2-year follow-up. This report adds to a growing body of evidence that describes the diverse and unpredictable nature of Type V dAVFs and highlights the need to obtain a cranial angiogram in pediatric patients with unexplained myelopathy and cervical cord T2 signal change on MRI 9).
Tanaka et al., described a case of the Cognard type V dAVF, draining into the spinal vein through the occipital sinus (OS) successfully treated by transarterial double catheter injection of Onyx. They used the alternating injections from 2 microcatheters until the Onyx reached the OS and reflowed into feeders adequately. This technique contributed to the elimination of the remaining afferent flow in an early stage of Onyx injection and achieved enough penetration into the draining vein 10).
Roelz et al., report a rare case of an intracranial dural arteriovenous fistula (DAVF) with perimedullary spinal venous drainage (Cognard Type V) that initially presented as a unilateral contrast-enhancing pontomedullary lesion mimicking a brainstem neoplasm in a 76-year-old man. Following occlusion of the DAVF by transarterial embolization that resulted in clinical and radiological improvement, the fistula recurred 10 months later and was finally cured by a combined endovascular and surgical approach that resulted in complete occlusion. Clinical symptoms and MRI findings gradually improved following this treatment. A literature review on the MRI findings of Cognard Type V DAVF was performed. Centrally located medullary or pontomedullary edema represents the typical imaging finding, while unilateral edema as seen in the authors’ patient is exceptionally rare. The hallmark imaging finding suggestive of DAVF consisting of perimedullary engorged vessels may not always be present or may only be very subtly visible. Therefore, they suggest performing contrast-enhanced MR angiography or even digital subtraction angiography in the presence of an unclear edematous brainstem lesion before scheduling stereotactic biopsy 11).
Aixut Lorenzo et al., described a patient in whom the first arterial treatment failed to achieve occlusion of the fistulous point with the glue. Clinical symptoms improved due to the diminished flow at the fistula after the first embolization but as soon as collateral arteries were recruited by the fistula, spinal cord venous drainage impairment led to symptoms recurrence. Transvenous access allowed them to close the fistula completely in one only session with a complete disappearance of the pathologically inverted perimedullary venous flow 12).