Surgical Treatment of Basilar Invagination without Evident Atlantoaxial Instability (Type B) - A Systematic Review

Chiari 1 malformation (CM1) and Basilar Invagination (BI) are the most common congenital bone and neural disorders of the craniovertebral junction. There is still discussion in the literature regarding best treatment practices for Type B BI. This systematic review aims to evaluate the treatment options for symptomatic type B BI especially concerning the need for craniocervical fusion. We performed a systematic literature review, focusing on surgical studies of patients with type B BI that reported the surgical technique used and the clinical outcomes. The MINORS instrument was utilized for methodological quality assessment as well as the level of evidence (LOL) of the included studies. Six studies were included, two of which used similar patients' samples. Posterior fossa decompression (PFD) with or without duroplasty was employed in three studies, C1-2 fusion in one, and C1-2 distraction and fusion in two studies. All reported patients' improvement post-surgery regardless of the technique used. Failure of PFD was associated with bone segmental anomalies in one study, and early deaths were associated with C1-2 fusion. The quality of the included studies was acceptable, with four studies at LOL 4 and two studies at LOL 3. There are varying surgical treatments for type B BI. PFD (most often with duroplasty) is safe and effective for patients without ventral compression. Some authors recommended C1-2 stabilization in all cases, and reported clinical improvement. Until prospective comparative studies, the ideal treatment option for type B BI remains unclear.