AN ANALYTICAL STUDY ON THE RESULTS OF POSTERIOR FOSSA DECOMPRESSION AND LAX DUROPLASTY IN CHIARI 1 MALFORMATIONS

...................................................................................................................... Introduction:Chiari 1 malformation has been approximately diagnosed in 1% to 4% of patientsundergoingbrainorcervicalspine magnetic resonance imaging (MRI) studies,1,2. Chiari malformation type 1 (CM-1) is a common and often debilitating neurosurgical condition. In recent years, there has been a growing emphasis on outcomes research, including efforts to compare the results of various surgical approaches.3,4 To help facilitate more objective comparisons,severalgroupshaveproducedand/or validated different metrics to evaluate treatment outcomes.5-8 However, despite this growing interest in improved research methodology, evidencebased guidelines for surgical intervention are undefined. The decision to treat CM-1 surgically may be based on a variety of considerations, such as anticipated syrinx improvement and stabilization of spinal cord damage, as well as the risk of postoperative complications. The objective of this study was to use clinical and neuroimaging features to predict long-term patient-reported Quality of life outcomes in patients undergoing posterior fossa decompressions.


Methods:-Patient population:-
This study is an analysis on the 28 patients evaluated and managed in our department of Neurosurgery in Govt Stanley medical college hospital, Chennai for Chiari 1 malformationsbetween 2011-2016.The study was proceeded following the approval from the ethical committee from our institution and consent from the patients.All patients had a detailed neurological examination followed by MRI scans of the brain with whole spine screening to evaluate the clinical presentations.Chiari 1 malformation patients had been graded based on the chiari severity index and underwent posterior fossa decompression with lax duroplasty.
Radiological analysis with MRI craniovertebral junction was used mainly to analyse the extent of descent of cerebellar tonsils and the size of the syrinx. In addition to these, we recorded the following neuroimaging parameters potentially related to CM-1 pathology: (1) tonsillar ectopia, as the perpendicular distance from the tipof the cerebellar tonsil to McRae's line9,10; (2) clivus-canal angle, as the angle between Wackenheim'sclivusbaselineandtheposteriorC2vertebralbodyline18; (3) dens angle, as the angle formed by a line through the C2 synchondrosis and a line through the odontoid tip measured from the posterior aspect of the C2 vertebral body11; (4) pB-C2, as the perpendicular distance between the ventral dura and a line joining the basion to the inferoposterior C2 body17,19,20; (5) obex position, as the distance between the obex and foramen magnum (basion-opisthion line)12; and (6) basilar invagination, as present when the tip of the dens was 5 mm above the Chamberlain's line. 11 We defined a syrinx a contiguousspinalcordcavitationmeasuringatleast3mminmaximum diameter on T2-weighted MRI.
Outcome assessment:-Weevaluated patient-defined outcome as improved, stabilised and worsened on the basis of postoperative follow up during the reviews. Any improvement from the presenting complains was considered as IMPROVED. Stabilised was defined as non-progression of complaints following the procedure. Any worsening of symptoms was to be taken as WORSENED.

Results and Discussion:-
Out of the total of 28 patients undergoing posterior fossa decompression for Chiari 1 malformation, the mean age of presentation was 24.5 years. 13 patients were male and 15 were female. Headache was the presenting complaint in all the 28 patients with classicialchiari type of headache in 24 and atypical presentation like generalised or fronto temporal headache in 4 patients. Based on these presentations, clinical grading was done as grade 1typical presentation, grade 2atypical presentation, grade 3predominance of myelopathic features. Table 3 shows the distribution of patients based on the clinical grading. Radiological grading was done on the basis of syrinx. If the diameter of the syrinx was greater than 6mm, it was grade B and if it was less than 6mm or absent, it was considered as grade A as shown in table 4 Postoperative outcome categorised as Improved (18 patients 64.2%), Stabilised (9 patients 32.1%) and worsened (1 patient 0.35%) as shown in table 5.

Conclusion:-
Posterior fossa decompression with lax duroplasty despite its complexity of the procedure is safe and effective way of reducing the symptomatology of chiari malformations with a lesser complication rate.