Anomalous posterior inferior cerebellar artery crossing the C1-2 facet in patient with atlanto-axial dislocation associated with down’s syndrome

Abstract

Dear Editor, Vertebral artery variations at the level of C1-2 have been documented, especially in patients with Down’s syndrome [5]. Additionally, cranio-vertebral junction (CVJ) anomalies are often seen in patients with Down’s syndrome [2]. The origin of posterior inferior cerebellar artery (PICA) at the level of C1-2 is one of the variations, with a reported incidence of approximately 1.1 % in normal population [4]. Of interest, such a variation of PICA has not been reported in CVJ anomaly with Down’s syndrome. It is important to identify such variation preoperatively to avoid complication during surgery for CVJ. A 7-year-old girl with Down’s syndrome presented with spastic quadriparesis that progressed over 6 months. X ray CVJ showed os-odontoideum with atlanto-axial dislocation reducing on extension (Fig. 1). Computed tomography (CT) Angiogram (2D and 3D reconstructed) images revealed the right PICA originating at the C1-2 level and crossing the joint space (Fig. 1). The patient underwent a posterior fusion. Intraoperatively, the bilateral C2 ganglion was cut. The vertebral artery (VA) could be seen coursing above the C1 arch, whereas the PICA was seen originating from VA between C1 and C2 transverse foramina and then crossing the C1-2 joint on the right side to course beneath the C1 arch. The vessel was carefully dissected, taking care not to injure it. The facetal surfaces were drilled lateral after retracting the PICA gently away from it. The lateral mass screws were inserted in C1, retracting the vessel gently to avoid injury. C2 pars-interarticularis screws were inserted and fused to C1 lateral mass screws. Bone grafts placed between the C1-2 joint and decorticated surface helped achieve a strong bony fusion. Her myelopathy improved significantly after 3 months. The PICA may originate extra-durally and extra-cranially in about 5–20 % [1]. An extradural PICA may arise just outside the dura at the CVJ or laterally above the transverse foramen of the atlas or between the transverse foramina of C-2 and C-1 [1]. In the normal population, the incidence of PICA originating between C2 and C1 transverse foramina is 1.1 % [4]. However, the incidence of other origins of PICA could not be localized in literature. Additionally, both CVJ and Vertebral artery (VA) abnormalities are more often seen in patients with Down’s syndrome as compared to those without it [2, 5]. Of interest, a anomalous PICA with CVJ abnormality in Down’s syndrome has never been described in the past. The variations in VA and origin of PICA is thought to be the result of variations in the development of the lateral spinal artery (LSA) and posterior spinal artery (PSA). The anterior or posterior location of the PICA (C2 origin) at the foramen magnum origin and the absence or presence of separate LSA help to distinguish the LSA from the PSA variant [3]. It has been suggested that chromosomal abnormality in Down syndrome contributes to VA abnormalities at CVJ [5]. After originating from the VA beyond the C2 transverse foramina, the PICA crosses across the posterior aspect of C1-2 joint to enter the dura at the level of C1. Such an origin and course of PICA makes it susceptible to injury during surgery, for the CVJ especially, while the C1-2 facet is being dissected, distracted and fixed with lateral mass screws. The abnormal PICA may be injured directly or its handling may tear its origin from the VA. Occasionally, the VA may end as this abnormal PICA [4]. The neurological damage due to PICA injury depends on the area it supplies. Although extradural PICAs do not send perforating branches to the anterior surface of the medulla P. Salunke (*) : S. Futane Department of Neurosurgery, PGIMER, Sector 12, Chandigarh, India 1600l2 e-mail: drpravin_salunke@yahoo.co.uk