Pediatric posterior cerebral artery stroke as a presentation of atlantoaxial dislocation.

We report an uncommon case of posterior circulation stroke in a young patient due to occlusion of posterior cerebral artery with reducible atlantoaxial dislocation (AAD). Plain dynamic radiography showed reducible AAD and intra-arterial digital subtraction angiography demonstrated occlusion of left posterior cerebral artery. Patient underwent stabilization of craniovertebral junction by occipito cervical fixation using occipit-C2/C3 lateral mass screws and rod fixation and has since experienced no recurrent symptoms. Vertebrobasilar insufficiency is a known entity in a patient with reducible AAD; however, isolated involvement of posterior cerebral artery is very rare. So this condition should be kept in mind, and necessary interventions must be undertaken at the earliest to avoid further irreversible brain damage.

Introduction

Atlantoaxial dislocation (AAD) is the most common bony craniovertebral junction (CVJ) anomaly followed by basilar invagination and occipitalized atlas.[1] AAD commonly present with progressive neurologic deficits due to compression of high cervical cord, lower brainstem and lower cranial nerves. Less commonly patient's with AAD may also present with neurologic symptoms attributable to vascular compromise at the CVJ.[1] The association between reducible AAD and vertebra-basilar insufficiency (VBI) has been well known and been well documented in the literature.[1] However, the posterior circulation stroke with isolated involvement of posterior cerebral artery in a patient with AAD is very rare. We report one such case with posterior circulation stroke as the initial presentation of AAD in a young patient.

Case Report

A 13-year-old male child presented with sudden onset of painless diminution of vision since 4 days, more in the left temporal visual field.

It was associated with occipital headache and dizziness. Patient also gave a history of clicking sounds in the neck on moving the neck. There was no history of recent trauma, transient ischemic attacks, seizures, weakness of limbs, gait ataxia or speech abnormalities.

On examination at the time of presentation, child was conscious, alert and oriented to time, place and person. Vitals were within normal limits. There was right homonymous hemianopia on visual field charting with macular sparing. There were no ocular abnormalities in the form of gaze palsy, internuclear ophthalmoplegia, nystagmus or skew deviation of the eyes. On motor system examination tone, bulk, power, and myotactic reflexes were normal with bilateral plantar being flexor. There were no sensory deficits and no cerebellar signs. Patient had neck tilt to the left side with low posterior hairline.

In view of above history and clinical findings, the possibility of stroke in young was considered and was evaluated with magnetic resonance imaging brain, which revealed left posterior cerebral artery territory infarct [Figure 1]. MR angiography revealed left PCA that was attenuated from its origin [Figure 2].

Figure 1

Axial T2-weighted (a), fluid attenuated inversion recovery (b) and diffusion weighted (c) magnetic resonance imaging showing infarct in the left posterior cerebral artery territory

Figure 2

Magnetic resonance angiographic brain showing attenuated left posterior cerebral artery

With the diagnosis of stroke, patient was started on antiplatelet therapy. Then the patient was thoroughly evaluated to find out the cause of stroke. All investigations including hemogram, coagulation profile, lipid profile, liver function test, renal function tests, erythrocyte sedimentation rate, X-ray chest were normal. Cardioembolism was excluded following a detailed cardiologic examination including electrocardiogram and echocardiogram, which were normal. Carotid Doppler studies were normal. Autoimmune markers including ANA, pANCA, acL IgG, acL IgM, C3, RA factor were normal. But patient's blood homocystiene level was 19 μmol/L (5–15), which was slightly on the higher side.

Moreover, in view of the patient being young with stroke without any obvious risk factors, with the presence of abnormal neck posturing and low posterior hairline, a possibility of an associated CVJ anomaly was entertained.

Dynamic X-rays of the cervical spine with CVJ revealed reducible AAD [Figure 3]. Non-contrast computed tomography cervical spine with CVJ showed occipitalized atlas with block vertebrae of C2/C3 and C6/C7 with mild kyphoscoliosis with AAD [Figure 4].

Figure 3

Flexion and extension X-rays of craniovertebral junction with cervical spine showing reducible atlantoaxial dislocation with block vertebrae of C2/C3 and C6/C7

Figure 4

Non-contrast computed tomography cervical spine showing occipitalized atlas with block vertebrae of C2/C3 and C6/C7

Intra-arterial Digital subtraction angiography was done which showed left PCA attenuated and shows complete block of distal branches with normal right PCA [Figure 5].

Figure 5

Intra-arterial digital subtraction angiography left vertebral injection showing attenuated left PCA

With the diagnosis of reducible AAD being made, patient was planned for stabilization of CVJ posteriorly. Patient underwent occipito-cervical fixation by Occipit-C2-C3 lateral mass screws and rod fixation. Postoperative radiograph showed adequate reduction of subluxation [Figure 6]. Postoperative period was uneventful and patient was discharged on 4th postoperative day with an advice to wear hard Philadelphia collar for 3 months. Patient was doing well at last follow-up of 6 months after surgery.

Figure 6

X-ray craniovertebral junction with cervical spine-after occipito cervical fixation

Discussion

The region of the craniovertebral junction, which includes the occipital bone and condyles, the atlas, and the axis, is unique from the remainder of the cervical spine with regard to its bony anatomy, joint shape and orientation, and relationship to the vertebral artery complex.[1] It is a transition between the cranium and the mobile cervical spine. The bony confines of the CVJ encompass the transition of the brainstem to the cervical spinal cord. This is the most mobile region of the cervical spine, and it functions as a “funnel” that is uniquely adapted to stability and motion.[1] CVJ instability may be congenital or secondary to a trauma or destructive lesion, such as infection or tumor. Defects in embryogenesis that occurs in the 3rd and 4th week of gestation can cause CVJ anomalies.[1]

Craniovertebral junction anomalies including skeletal and soft tissue elements are more common in Indian subcontinent compared to western countries.[2] Of the skeletal CVJ anomalies, AAD is most common in India followed by occipitalization of atlas, and basilar invagination, whereas basilar invagination is most common in the western countries.[2]

The most common anomalies occurring in combination in India are AAD, occipitalization of atlas, and block vertebrae of C2 and C3.[2] The CVJ anomalies are usually congenital and occur since birth, but the mean age of manifestation is around 25 years. Males are most commonly affected.[2] Predisposing factor in the form of trivial neck trauma may be identified in nearly 50% of the cases.[2]

Our patient was a male and first became symptomatic at 13 years of age, but there was no history of preceding neck trauma or manipulation. CVJ anomalies commonly present with progressive neurologic deficits due to compression of high cervical cord, lower cranial nerves, and brainstem.[3] Upper cervical spinal cord damage can manifest in the form of pain, sensory or motor disturbances, proprioceptive derangement, gait imbalance, abnormalities in coordination, and respiratory insufficiency.[3]

Vascular occlusive syndromes of the posterior circulation affecting the vertebrobasilar circulation also occur in CVJ anomalies, and it may arise from an arterial dissection (intra-or extracranial), leading to thrombus and embolism.[3] Apart from the well-known syndrome of VBI, which is characterized by a complex array of symptoms, including ataxia, drop attacks, vertigo, nausea and vomiting, diplopia, dysarthria, tinnitus, and visual disturbances, vertebral artery insufficiency is also known to contribute to high cervical myelopathy (due to recurrent low-grade compression of the anterior spinal artery).[4567] Acute deterioration leading to sudden death has also been documented due to vertebral artery occlusion.[8] Posterior circulation infarcts in congenital CVJ anomalies are possibly secondary to chronic low-grade microtrauma leading to intimal damage of vertebral arteries due to repeated flexion-extension of the vessel, resulting in platelet aggregation, thrombus formation, and embolization with blockage of vertebrobasilar circulation.[9]

Our patient however presented as a case of young-onset posterior circulation stroke with sudden onset of diminution of vision associated with headache and dizziness. Embolism of a thrombus from vertebral artery to posterior cerebral artery with resultant ischemia is the most likely pathogenesis in our case.

The association of VBI with CVJ anomalies remains very much underestimated, with one study showing that only 11% of the patients with VBI have appropriate dynamic (flexion and extension) cervical radiographs performed.[10] This finding implies that a large proportion of patients with VBI may well in fact have CVJ anomalies that remain undiagnosed and hence not treated. However, posterior circulation stroke involving isolated posterior cerebral artery without involvement of vertebrobasilar complex, as the presentation of CV junction anomalies, as was observed in our case, is extremely rare. The clinical infrequency of posterior circulation territory infarcts in congenital CVJ anomalies has been traditionally attributed to the double blood supply through the two vertebral arteries and the adequacy of the circulation of Willis, which prevents a full-fledged infarct from developing in these patients.[11] However, it is thought that this spuriously low occurrence may possibly be because patients symptomatic for VBI are not routinely evaluated for CVJ anomalies and, therefore, stay undiagnosed.

Atlanto-axial dislocation,[1213] is the most common CVJ anomaly that has been implicated in causation of posterior circulation stroke or VBI, followed by odontoid aplasia,[10] basilar invagination, occipitalization of the atlas, Klippel-Feil anomaly, and anomalous osseous process of the occipital bone projecting to the posterior arch of the atlas.[14] Our patient also had atlanto-axial dislocation in conjunction with occipitalization of the atlas and C2-3 block vertebra with posterior circulation stroke.

In most reports of CVJ anomalies with posterior circulation stroke, cerebellar infarction is common but multiple areas supplied by the vertebro-basilar system can be affected, but this was not observed in our case. Our patient had only infarct in the occipital lobe without involvement of the cerebellum, which is much more rare.

Conclusion

Clinicians should be aware of the rare clinical presentations of CVJ anomalies. All young patients presenting with features of VBI or posterior circulation stroke should be screened for CVJ anomalies.