INTRODUCTIONNeurofibromatosis is a dysplasia of mesodermal and

neuroectodermal tissues with potential for diffuse systemic

involvement. Many vascular anomalies are associated with

neurofibromatosis. Arteriovenous fistulas are abnormal com-

munications of the artery and vein and, although commonly

traumatic in aetiology, they might occur spontaneously. Ver-

tebral arteriovenous fistulas are uncommon in neurofibro-

matosis, more so in combination with atlantoaxial dislocation.

Both the conditions are potentially treatable and recognition of

this association has therapeutic implications.

CASE REPORTA 30-year-old woman presented with progressive paraparesis

for duration of 3 months preceded by neck pain of 15 days. She

had a loss of bowel and bladder control. On examination,

multiple hyperpigmented patches were seen on her body. Few

cutaneous nodules (~8–10) were also noted over her trunk.The

deep tendon reflexes were absent with loss of sensation over

the extremities. There was a near-complete loss of muscle

power. A radiograph of the neck was performed and showed the

presence of atlantoaxial dislocation. For a better evaluation of

the changes to the spinal cord, she underwent an MRI of the

cervical region. This confirmed the presence of an atlantoaxial

dislocation with narrowing of the spinal canal at the C1–C2 level

(Figs 1,2). There was hyperintense signal in the cord extending

from the level of C1 to C6 cervical vertebral segments on T2-W1

images appreciated on both sagittal and axial images (Fig. 1).

Numerous serpentine hypointense flow-void channels were

seen ventral and lateral to the cord, causing extradural

Case Report

Magnetic resonance imaging findings in an unusualcase of atlanto axial dislocation and vertebralartery–vein fistulas in a patient ofneurofibromatosis-1Sharad Maheshwari,1 Hrishikesh A Kale,2 Shrinivas B Desai2 and Anirudh Kohli2

1University of Toronto, Toronto, Canada, and 2Department of Radiology and Imaging, Jaslok Hospital and Research Centre, Mumbai, India

SUMMARY

Vertebral arteriovenous fistulas are uncommon in neurofibromatosis. We describe MRI findings of a patient with anunusual association of bilateral vertebral arteriovenous fistulas with an atlantoaxial dislocation in the setting ofneurofibromatosis.

Key words: atlantoaxial dislocation; bilateral vertebral arteriovenous fistulas; neurofibromatosis-1.

S Maheshwari MD; HA Kale MD; SB Desai MD; A Kohli MD.

Correspondence: Dr Sharad Maheshwari, University of Toronto, 2203 Wood Street, Toronto, ON, Canada M4Y2P8. Email: sharraddoc@hotmail.com

Submitted 1 May 2001; resubmitted 13 November 2001; accepted 3 December 2001.

Australasian Radiology (2002) 46, 316–318

Fig. 1. T2W sagittal images show multiple flow voids, hyperintense

signal in cord secondary to ischemia and narrowing of spinal canal at

C1–2 level secondary to atlanto axial dislocation.

317NEUROFIBROMATOSIS-1 MRI FINDINGS

Fig. 4. T2W coronal MRI showing serpentine collaterals as flow voids.

Fig. 2. T2W axial MRI showing atlanto axial dislocation.Fig. 3. T2W axial MRI showing flow void channels from the vertebro-

venous fistula with both intra- and extra-spinal components.

Fig. 5. Contrast enhanced MR angio showing filling of venous col-

laterals during the arterial phase, suggesting fistulous communication.

318 S MAHESHWARI ET AL.

compression of the cord.Vertebral arteries were dilated on both

sides. Flow-void vascular channels were seen extending from

the neural canal with both intra- and extraspinal components

(Figs 3,4). Contrast-enhanced study and 2-D TOF angiography

(flow up) and a phase-contrast angiogram with velocity was

subsequently performed showing these areas to be vascular

channels consisting of high-flow collaterals, suggesting fis-

tulous communication between the vertebral artery and the

vertebral vein (Fig. 5). Magnetic resonance angiogram was

important to decide the caudocranial flow as well as to deter-

mine the velocity in these vascular channels. An angiogram was

performed, and confirmed these findings. The patient under-

went coil embolization of the fistulous channels. The patient’s

neurological status is being actively monitored.

DISCUSSIONNeurofibromatosis is an autosomal-dominant genetic disease,

characterized by the presence of cafe au lait spots, neuro-

fibromas and several bony anomalies.1 Deformities of the spine

are the most frequent alterations. Involvement of the cervical

spine has been studied less frequently. It is associated with

abnormalities of the long arm of chromosome 17. Plexiform

neurofibromas are a hallmark of NF-1 and are diagnostic of

von Recklinghausen Neurofibromatosis.1 These neurofibromas

are typically isointense to the muscle on T1-W1 images, hyper

intense on T2-W1 and enhance strongly on contrast admini-

stration.1–3 The renal and gastrointestinal systemic vascular

lesions are common; however, involvement of the craniocere-

bral vessels is relatively rare. More than 85% of the reported

cerebrovascular lesions are occlusive or stenotic in nature.

Aneurysms are the second most common vascular abnormality

in NF-1. Non-aneurysmal vascular ectasias and arteriovenous

fistulas or malformations occur less frequently. Atlantoaxial

dislocation results from an insufficiency or absence of the trans-

verse ligament that normally holds the odontoid to the anterior

arch of the atlas.This is measured as the distance between the

posterior surface of the anterior arch of atlas and the anterior

surface of the odontoid process. An atlantodental distance

greater than 2.5 mm in adults and 5 mm in children is con-

sidered to be unstable.4 The pathogenesis of atlanto-

axial dislocation in neurofibromatosis is uncertain, basilar

impression might occur secondary to the loss of bone mass of

the lateral masses of the atlas. Magnetic resonance imaging is

useful in determining the extent of the neural involvement, and

is the non-invasive modality of choice. Spinal-cord changes

result from venous hypertension, causing ischaemia.2 Flow

voids depict the enlarged feeding and draining vessels of

the arteriovenous fistula. Mass effect of the enlarged vascular

structures with displacement or distortion of the cord might

occur. Intrinsic cord-signal abnormality and evidence of

haemorrhage might be present. The small size of some lesions

and lack of nidus might make detection, even by MRI, difficult.

Angiographic evaluation of arteriovenous fistula is essential for

the complete delineation of the angioarchitecture, especially to

determine the exact location of the fistula. Endovascular treat-

ment consists of a complete occlusion of the fistula and

proximal part of the draining vein.2 Atlantoaxial dislocation and

involvement of the cervical spine has been studied less

frequently.

Multiple neurofibromas in the craniocervical junction

appeared to be the cause of the atlantoaxial dislocation in this

patient, and the dislocation might have contributed to the

formation of the bilateral vertebral arteriovenous fistulas.

Hasegawa H et al.5 reported a similar case in which there was

presence of vertebral artery and vein fistula in the setting of

neurofibromatosis and atlantoaxial dislocation. We feel that

the present case might be similar to this extremely rare condition.

Atlantoaxial dislocation has received little attention in many

studies of spinal deformity in neurofibromatosis.Very few reports

of atlantoaxial dislocation in association with neurofibromatosis

have been published.6,7 Isu et al.,7 in a later paper, postulated that

the cause of the atlantoaxial dislocation might be the result of

the presence of neurofibromas at the atlantoaxial junction and, in

some, the result of mesodermal dysplasia.7,8 Both the presence

of flowing blood and calcification give a hypointense appearance

on T1-WI and T2-WI; therefore, a contrast-enhanced MRI and an

MR angiography study are extremely essential in the evaluation

of this condition. Presence of hypointense areas on axial images

might lead to a false impression of calcification.

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