Successful Treatment of Basilar Invagination and Platybasia Associated With Cerebellar Atrophy by Decompression Surgery

Abstract

Dear Editor, Craniovertebral junctional abnormalities are rare but underrecognized developmental disorders of the neural axis. The associated conditions include basilar invagination and platybasia, for which there have been only a few related clinical reports,1 and so the possible pathomechanisms remain unclear. Here we present a case of successful recovery from basilar invagination, platybasia, and cerebellar atrophy after decompressive surgery. A 41-year-old female patient presented to the clinic with a 2-year history of progressive imbalance. She also complained of voice changes, swallowing difficulties, and dizziness aggravated by upright posture. The patient had no familial loading or developmental delay, and no history of head or neck trauma. A neurological examination revealed dysarthria, dysphagia, gaze-evoked horizontal nystagmus augmented by left gaze, impaired left-sided smooth pursuit with preserved saccades (Supplementary Video in the online-only Data Supplement), and truncal ataxia with veering tendency to the right side. Her motor and sensory functions remained intact. Laboratory evaluations such as inflammation, infection, endocrine, and paraneoplastic antibody tests all produced negative findings. Magnetic resonance imaging (MRI) of the brain and cervical spine showed complete atlanto-occipital assimilation with severe basilar invagination and platybasia, resulting in anterior medullary compression and tonsillar herniation (Fig. 1A and B). Severe cerebellar atrophy was observed, predominantly in the bilateral vermis (Fig. 1D and E). Applying posterior fossa decompression and C1 laminectomy with duroplasty improved the imbalance and bulbar symptoms, including hoarseness and dysphagia, while postsurgery MRI revealed good decompression (Fig. 1C and F). Previous reports on basilar invagination have focused on surgical outcomes, which vary.2,3 Chronic vascular insufficiencies and tonsillar herniation have been suggested as underlying pathomechanisms.1 However, the treatments applied for anatomical decompression do not always result in good clinical outcomes.3 Therefore, understanding the neuroanatomical basis for the development of a patient’s symptoms is critical to achieving an accurate diagnosis and effective treatment. In the present case, magnetic resonance angiography revealed no particular stenosis or occlusion of the cerebral blood vessels. Although the anterior medulla was anatomically compressed, the symptoms and signs of the patient imply that the dorsal medulla, including the nucleus prepositus hypoglossi4 and vestibular nuclei, may play primary roles in provoking symptoms. The dorsal part of the medulla abutting the fourth ventricle, known as the area postrema, showed sparse tight junctions in the blood–brain barriers,5 which may contribute to a sensitivity to mechanical stress due to the obtuse angulation of platybasia, like in the present case. Since decompressive surgery not only releases local compression but also alleviates crowding among infratentorial structures or ventricuJuhee Lee Hyung Seok Guk Museong Kim Eung-Joon Lee