The relationship between Chiari 1.5 malformation and sleep-related breathing disorders on polysomnography

OBJECTIVE Chiari 1.5 malformation is a subgroup of the Chiari malformation in which tonsillar descent into the foramen magnum is accompanied by brainstem descent. No data exist on whether operative decompression in patients with Chiari 1.5 improves sleep-related breathing disorders (SRBDs) and whether there are radiological parameters predicting improvement. METHODS The authors performed a retrospective cohort study of consecutive pediatric patients with Chiari 1.5 malformation and SRBDs at the Alberta Children's Hospital. An SRBD was characterized using nocturnal polysomnography (PSG), specifically with the apnea-hypopnea index (AHI), the obstructive apnea index, and the central apnea index. Pre-operative values for each of these indices were compared to those following surgical decompression. The authors also compared preoperative radiographic factors as predictors to both preoperative AHI and the change in AHI with surgery. Radiological factors included tonsillar and obex descent beneath the basion-opisthion line, the presence of syringomyelia, the frontooccipital horn ratio, the pB-C2 line, and the clivoaxial angle. RESULTS Seven patients (5 males, 2 females) met inclusion criteria. One patient had two surgical decompressions, each with pre-and postoperative PSG studies (n = 8). The median age was 9 years. Before surgical decompression, 75% underwent tonsillectomy/adenoidectomy. The majority (87.5%) experienced snoring/witnessed apnea preoperatively. The median tonsillar and obex descent values were 21.3 mm and 11.2 mm, respectively. The median values for the pB-C2 line and clivoaxial angle were 5.4 mm (interquartile range [IQR] 4.5 mm, 6.8 mm) and 144 degrees (IQR 139 degrees, 167 degrees), respectively. There was a statistically significant change from preoperative to postoperative AHI (19.7 vs 5.1, p = 0.015) and obstructive apnea index (4.5 vs 1.0, p = 0.01). There was no significant change in the central apnea index with surgery (0.9 vs 0.3, p = 0.12). No radiological factors were statistically significant in predicting preoperative AHI and change in AHI. CONCLUSIONS This is the first series of pediatric patients with Chiari 1.5 with SRBDs who demonstrated a marked im- provement in their PSG results postdecompression. Sleep apnea has a significant impact on learning and development in children, highlighting the urgency to recognize Chiari 1.5 as a more severe form of the Chiari I malformation.