Atlantoaxial Subluxation Secondary to Unstable Os Odontoideum in a Patient With Arrested Hydrocephalus Due to Congenital Aqueductal Stenosis: A Case Report

Abstract

Background: In a small percentage of children born with congenital hydrocephalus, enlargement of the head and the presence of ventriculomegaly may halt and ultimately stabilize the condition designated as arrested hydrocephalus. Arrested hydrocephalus in children is typically due to congenital aqueduct stenosis, which can be described appropriately as a stasis existing within the channel between the third and fourth ventricles. Os odontoideum (OO) is an uncommonly occurring pathology at the craniovertebral junction. Although the clinical and radiologic features of its existence and the therapeutic options for its pathology have been widely discussed within the medical literature, its true etiology has been a source of divisive debate, proposing both a traumatic as well as a congenital mechanism. The etiology of OO has been heartily debated in the literature for several years as well. Most authors have come to support a posttraumatic causality. However, strong evidence exists to support a congenital origin to this rarely observed malformation. Methods: Within this case study we present a 24-year-old woman with atlantoaxial subluxation that exists secondary to an orthotropic OO. The patient had a history of arrested hydrocephalus due to congenital aqueductal stenosis beginning in early childhood. She presented with normal intelligence and was neurologically without deficits before the occurrence of an atlantoaxial dislocation. Unfortunately, the pathology was initially misdiagnosed as a decompensation state of the arrested hydrocephalus, and after 8 months the patient became wheelchair bound. Following this unfortunate event the correct diagnosis was ultimately uncovered. Subsequently a C2-1 instrumentation procedure resulted in excellent alignment and fusion. Conclusions: To the best of our knowledge, this is the first example of an aqueduct stenosis in the setting of an existing OO, a combination that might be another clue in favor of a congenital etiology.

Unstable os odontoideum contributing to cervical myelopathy and obstructive sleep apnea

“…[1] Alternative surgical options include C2- C1 transarticular fixation, application of a translaminar C2 screw instead of a C2 pedicle screw, and the use of an atlas hook instead of a C1 lateral mass screw. [9,10,12] Adequate management of instability with relief of C1-C2 cord/brain stem compression may allow for symptoms of OSA to resolve.…”

“…Os odontoideum (OO), a traumatic or congenital abnormality of the second cervical vertebrae, is characterized by a separate bony segment with a smooth circumferential margin. [9,10,12] Here, the authors describe a 36-year-old male who developed OSA and a progressive quadriparesis attributed to an unstable OO. Following reduction and stabilization, both his quadriparesis and OSA improved.…”

Double-level myelopathy due to atlantoaxial dislocation (os odontoideum) and subaxial cervical spondylosis with angular kyphosis

“…[8,9] e management of symptomatic OO with reducible atlantoaxial instability has evolved to now using either a C1-2 screw rod fixation or the Harms technique. [4][5][6][7][8]…”

“…Unstable os odontoideum (OO) with atlantoaxial dislocation and subaxial "draping of the cervical spinal cord" over a kyphotic deformity contributed to dual-level significant cord compression and myelopathy in a 78-year-old male. [1][2][3][4][5][6][7][8][9][10][11] Following a 540° anterior-posterior-anterior decompression and fusion, the patient improved.…”