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Ventral brain stem compression in pediatric and young adult patients with Chiari I malformations
P A Grabb1, T B Mapstone, W J Oakes
1Department of Surgery, University of Alabama at Birmingham, Children's Hospital of Alabama, 35233, USA.
Insights
Ventral brain stem compression (VBSC) in Chiari I malformations can be objectively measured. A measurement below 9 mm indicates successful treatment with posterior fossa decompression alone for VBSC.
Area of Science:
- Neurosurgery
- Pediatric Neurology
- Radiology
Background:
- Chiari I malformation involves cerebellar tonsil descent.
- Ventral brain stem compression (VBSC) is a potential complication.
- Objective measurement of VBSC is needed to guide treatment.
Purpose of the Study:
- Determine the incidence and degree of VBSC in pediatric and young adult Chiari I patients.
- Correlate VBSC with imaging and clinical factors.
- Identify VBSC thresholds for successful posterior fossa decompression alone.
Main Methods:
- Analysis of MRI and clinical histories in 40 pediatric/young adult Chiari I patients.
- Subjective grading of VBSC and measurement of tonsillar descent.
- Objective VBSC measurement using the pB-C2 distance on sagittal MRI.
Main Results:
- 48% and 28% of patients showed ventral brain stem flattening and distortion, respectively.
- pB-C2 measurements correlated with subjective VBSC grade, age, and tonsillar descent.
- Patients with pB-C2 < 9 mm had successful outcomes with posterior fossa decompression alone.
Conclusions:
- A pB-C2 measurement < 9 mm suggests VBSC is not a limiting factor for posterior fossa decompression.
- For pB-C2 measurements ≥ 9 mm, addressing VBSC may be necessary prior to decompression.
- Objective VBSC measurement aids in surgical planning for Chiari I malformation.
Objective:
The purposes of this study were as follows: 1) to determine the incidence and degree of ventral brain stem compression (VBSC) in pediatric and young adult patients with Chiari I malformations, and 2) to correlate VBSC with other imaging and clinical factors to help determine what amount of VBSC is successfully treated with a posterior decompressive procedure alone.
Methods:
The magnetic resonance images and clinical histories of 40 pediatric and young adult patients with Chiari I malformations were analyzed for subjective grade of VBSC, distance of tonsillar descent, odontoid's relation to Chamberlain's and Wackenheim's line, clival length, foramen magnum diameter, syringomyelia, scoliosis, hydrocephalus, presenting clinical status, treatment, and outcome. To objectively measure the amount of ventral cervicomedullary encroachment by the odontoid and its investing tissues into the rostral spinal canal, a line (B-C2) was drawn between the basion and posteroinferior aspect of the C2 body on a sagittal magnetic resonance image. A line perpendicular to this line, pB-C2, was drawn through the odontoid tip to the ventral dura, and a distance (representing the amount of ventral canal encroachment) was measured.
Results:
Flattening and distortion of the ventral brain stem were present in 48 and 28% of the patients, respectively. Only two patients had basilar invagination by traditional definitions. pB-C2 measurements correlated with the subjective grade of VBSC (P < 0.05), age, and distance of tonsillar descent (P < 0.05). Eye motion abnormalities and upper cervical osseous anomalies were associated with higher pB-C2 measurements. All patients with a pB-C2 measurement of less than 9 mm were treated successfully with posterior fossa decompression alone despite any subjective VBSC. Some patients with pB-C2 measurements greater than 9 mm had either preoperative neurological deficits or neurological worsening after posterior fossa decompression referable to VBSC.
Conclusion:
Patients with a pB-C2 measurement of less than 9 mm do not require treatment directed at VBSC. In select patients with pB-C2 measurements of 9 mm or greater, reduction of VBSC may be prudent before posterior fossa decompression.