Trigeminal hypoplasia due to vertebrobasilar dolichoectasia: A new entity

Abstract

The term “vertebrobasilar dolichoectasia” refers to anomalous dilatation of the intracranial arteries associated with elongation or tortuosity of the affected vessels. The etiology of the disease is unknown and is usually detected incidentally. The predominant clinical manifestations arise due to the mass effect of the dilated vessels and may include cranial nerve compression, extrinsic aqueductal compression, motor and sensory disturbances. Trigeminal hypoplasia is a very uncommon condition, usually described in association with Goldenhar-Gorlin syndrome and has not yet been attributed to vertebrobasilar dolichoectasia. The current case report highlights this rare association of trigeminal nerve hypoplasia and vertebrobasilar dolichoectasia, leading to hemifacial and corneal anesthesia.

Introduction

Vertebrobasilar dilochoectasia is an extremely rare vascular pathology characterized by increased length and caliber of intracranial arteries with an expected incidence of 0.06–5.8%.[1,2] The disorder mainly affects the vertebral and the basilar arteries. Trigeminal nerve hypoplasia is a rare entity characterized clinically by unilateral hypoesthesia of face and corneal insensitivity. Few cases of trigeminal neuralgia due to vertebrobasilar dolichoectasia have been described in literature. However, in none of the cases a hypoplastic trigeminal nerve was demonstrated, and none of these cases were reported in pediatric patients. In the current case report, dolichoectatic vertebral artery associated with trigeminal nerve hypoplasia was adequately revealed on imaging.

Case Report

An 11-year-old male patient from the rural background consulted the ophthalmology OPD with loss of sensations over the left half of the face and the cornea since birth and reduced visual acuity.

The patient also complained of occasional deviation of the tongue during speaking and chronic pulsatile headache especially in morning. On examination, the vitals of the patient were stable, and general examination of the patient was uneventful except for pallor. Neurological examination revealed hypoesthesia along the left side of the face corresponding to ophthalmic, maxillary and mandibular divisions of the trigeminal nerve. There was corneal anesthesia with corneal ulceration. Rest of neurological examination was normal. The patient was then referred for contrast-enhanced computed tomography scan of the head, which revealed abnormally dilated and tortuous left vertebral artery, with an aberrant course. The caliber of the vertebral artery was 7.2 mm and it was seen compressing the left lateral aspect of the brainstem, with relative atrophy of the anterosuperior part of the left cerebellar hemisphere leading to dilation of ipsilateral cerebellopontine angle cistern and crossing toward the right side [Figure 1]. The ectatic vessel was also seen compressing the fourth ventricle with mild dilatation of bilateral lateral ventricles.

Figure 1.

(a) Axial contrast-enhanced computed tomography scan of the head showing dilated left vertebral artery (black arrow), with an elongated aberrant course seen crossing toward the right side (white arrow). (b) At the next consecutive cranial scan, note the atrophy of the anterosuperior part of the left cerebellar hemisphere with widened cerebellopontine angle cistern (black arrow). The anomalous crossed left vertebral artery is now lying at the right side anterior to the midbrain (white arrow)

No definite evidence of thrombosis was seen, and the rest of the brain parenchyma was normal at the time of the scan. For further work up of the disease etiology, patient underwent magnetic resonance imaging (MRI) of the head with magnetic resonance angiography (MRA). MRI of the brain showed the abnormally dilated vessel to be the left vertebral artery, with evidence of compression of the left inferior olivary nucleus causing its flattening and the brachium pontis [Figures 2a and b, 3]. Application of constructive interference in steady state sequence revealed that the ectatic vessel was associated with left-sided trigeminal nerve hypoplasia, with marked thinning of the preganglionic cisternal segment of the trigeminal nerve. The Meckel's cave and the porus trigeminus were empty [Figure 4]. Also noticed was mild displacement of the left facial nerve by the ectatic vertebral artery [Figure 4]. Rest of the visualized cranial nerves appeared normal. MRA showed that the left vertebral artery was unduly prominent, with an aberrant course having an anomalous high union with the left branch of the right vertebral artery at the level of brachium conjunctivum [Figure 5]. There was associated atrophy of the lingula and lobulus centralis on the left side leading to prominent cerebellopontine angle cistern [Figure 4]. The patient was reassured and was advised keratoplasty for correction of corneal ulcer. Being congenital in nature, the pathology was deduced to be nerve hypoplasia rather than nerve atrophy.

Figure 2.

(a) Sagittal and (b) Coronal T2-weighted magnetic resonance imaging showing ectatic aberrant left vertebral artery in the prepontine cistern

Figure 3.

(a) Axial T2-weighted magnetic resonance imaging image showing anomalous course of the left vertebral artery, with compression and flattening of the left inferior olivary nucleus (black arrow). (b) Axial constructive interference in steady state sequence showing crossing of the anomalous left vertebral artery (black arrow)

Figure 4.

(a) Axial constructive interference in steady state sequence image showing hypoplastic left preganglionic cisternal trigeminal nerve (white arrow), with normal right trigeminal nerve (black arrow). (b) The left facial nerve appears stretched by the ectatic left vertebral artery (black arrow). Also note that the meckel's cave and the porus trigeminus are empty (white arrow)

Figure 5.

(a and b) Time of flight magnetic resonance angiography showing dolichoectatic left vertebral artery. Note that there is no confluence of vertebral arteries and no basilar artery is seen. The posterior cerebral arteries are not distinctly visualized. (c) Further evaluation through the constructive interference in steady state sequences revealed bifurcation of the right vertebral artery (black arrow) with anomalous high union of the left vertebral artery with the left branch of the right vertebral artery at level of brachium conjunctivum (not shown in figure)

Discussion

Vertebrobasilar dolichoectasia has been associated with extrinsic cranial nerve compression, obstructive hydrocephalus, motor and sensory disturbances. The disorder is more common in males and is seen usually in 6^th–7^th decade of life. The criteria for dolichoectasia include a diameter of more than 4.5 mm, basilar length >29.5 mm or intracranial vertebral artery length >23.5 mm[3] and deviation of the ectatic vessel of more than 1 cm beyond the shortest normal course.[3,4] The criteria for elongation include bifurcation of the basilar artery above the suprasellar cistern or if the basilar artery lies lateral to dorsum sellae or margin of clivus.[3] It usually affects the basilar artery alone (40%), and less commonly bilateral vertebral arteries, basilar artery (22%) and both vertebral arteries (16%).[4] Compression of cranial nerves can result in hemifacial spasms, trigeminal neuralgias (C.N. 5), vision loss (optic tract involvement) and nystagmus. In few reported cases of vertebrobasilar dolichoectasias complicated by trigeminal neuralgia, hypoplasia of the trigeminal nerve has never been reported, rather the condition was associated with compression of the root entry zone of the trigeminal nerve. In our case, the symptomatology of hemifacial anesthesia corresponded well with the imaging findings. Vertebrobasilar dolichoectasia has never been described as a causative factor of trigeminal nerve hypoplasia and has never been associated with congenital hemifacial anesthesia so far.

Another uncommon finding in our case was mild obstructive hydrocephalus, which was caused due to compression of the fourth ventricle by the ectatic vertebral artery that was seen causing atrophy and compression of the left brachium pontis. This hydrocephalus has also been described as having “Water-Hammering effect” due to the pulsatile blood flow in the ectatic vessel.

Management of vertebrobasilar dolichoectasia depends upon the clinical picture. In cases associated with obstructive hydrocephalus, ventriculo-peritoneal shunting may be required to relieve the obstruction. As with idiopathic trigeminal nerve hypoplasias, the treatment of trigeminal hypoplasia caused by vertebrobasilar dolichoectasia revolves around the care of eyes and treatment of keratoconjunctivitis due to corneal anesthesia. Steroids, antibiotics and eye patching and ointments are given for symptomatic relief, and regular follow-up is recommended.

Conclusion

Vertebrobasilar dolichoectasia should be considered as a differential in cases of trigeminal nerve hypoplasia and also in cases of obstructive hydrocephalus not explained by other causes.