Chiari Type 1[C1M] malformation is a disorder or deformity of varied causes associated with descent of the cerebellar tonsils at least 4mm below the level of the foramen magnum [1-3]. The causes of C1M are primary and secondary. In primary type, the condition arises de novo while in secondary type, it is associated with “push” factors such as hydrocephalus, brain tumours or other causes of raised intracranial pressure, as well as “pull” factors such as tethered spinal cord and lumbar peritoneal shunts [1-3]. There has been, over the past 40 years, significant evolution in the approach to C1M and its management, from it being thought of as a degenerative disease with no surgical remedies, to radiotherapy being considered appropriate, to the current era where a deeper understanding of its possible aetiologies and multiple corrective surgical options exist [4].

C1M can be an incidental finding in asymptomatic individuals while in others, there may be sub-occipital headaches typically worsened by Valsalva type manoeuvres, deficits of lower cranial nerves and long tract spinal cord signs in instances where syringomyelia complicates the condition [1-3,5].

Syringomyelia, also referred to as syrinx, is a condition in which fluid accumulates in the substance of the spinal cord; depending on the degree to which this happens, the individual may be asymptomatic at one end of the spectrum or severely disabled at the other end [5-7]. Syrinx formation is the most serious consequence of C1M and the one most likely to cause long term sequelae and undermine the quality of life of the affected individual. Hence, the fate of syringomyelia in individuals undergoing surgery for C1M is a matter of great interest. There are various techniques described for the treatment of C1M [2,4]. These include bony decompression only of the foramen magnum with possibly a laminectomy of the first and sometimes second cervical vertebra, posterior fossa decompression and duroplasty [PFDD] with/without arachnoid dissection, posterior fossa decompression with splitting of the outer layer of the dura, and PFDD with tonsillar resection [8-10]. In addition, atlanto-axial fusion has been proposed as a treatment for this, although being a more recent development compared with then other established options, long term follow up data are not yet available for this technique [11-14].

Studies have found no difference in outcome of the syrinx with PFDD regardless of whether or not arachnoid dissection was carried out but where only splitting of the outer layer of dura was done, the result was not as good as the former techniques [8]. Regarding the cerebellar tonsils, there was no discernible difference in syrinx outcome whether these were sacrificed or left intact [9]. Some studies have shown that posterior fossa decompression may not improve the clinical or radiological outcome of syringomyelia in 40% to 50% of patients where persistence, progression, or recurrence of syringomyelia occurs [15] and re- decompression or ventricular shunting procedures have high failure rates [16]. Nevertheless, where there is radiographic failure but good symptom control, a conservative approach is recommended [16]. Contrary to these dismal figures, another study found that following PFDD for C1M, syringomyelia improved in 91.3%, worsened in 3.7% and remained unchanged in the rest [10]. These widely divergent outcomes for the same procedure in different hands suggest that the individual techniques applied by different surgeons at their respective centres for what is supposedly the same operation, as well as differences in follow up may play a big role in what is reported. One aspect that must be considered is the question of the presence of hydrocephalus. In 7-10% of cases of C1M, hydrocephalus is present. 

Where this is the case, the treatment of the hydrocephalus by endoscopic third ventriculostomy has been shown to result in relief of hydrocephalus, tonsillar descent and syringomyelia in 90.5%, 78.5% and 76% respectively of cases [17]. Considering the foregoing, it would appear prudent to suggest that where hydrocephalus exists in the setting of C1M, this should be addressed first. Where this does not obtain, then posterior fossa decompression with or without tonsillar sacrifice and subarachnoid dissection should be offered. In the event of failure of the syringomyelia to resolve and especially if this is symptomatic, then re-do PFDD, atlanto-axial stabilization, as well as syringo-peritoneal or syringo-subarachnoid shunts may be tried [15,16].

C1M associated with hydrocephalus and complicated by syringomyelia has been treated with cerebrospinal fluid diversion alone, by either endoscopic third ventriculostomy or ventriculoperitoneal shunting with good reported results in as far as resolution of the clinical features and radiological picture are concerned [17]. This case described is an exception, as she failed to respond to this line of treatment. She did do very well with PFDD procedure, which itself has had widely differing outcomes reported by different groups [10,15]. This case illustrates the fact that a single procedure may not be the solution to every case and further research is indicated to establish the most likely surgical procedure to be of benefit in a given case of C1M, to avoid the need for multiple procedures.