Chiari Malformation & Syringomyelia In Neurofibromatosis Type I: An Under-recognised Association 

Caroline Parkin1,  Alisdair McNeill2  

  1. Specialty Registrar in Radiology, North West of England training scheme.

  2. NIHR Academic Clinical Fellow, Clinical Genetics Unit, Birmingham Women’s Hospital, Edgbaston, Birmingham. B15 2TG.

Correspondence to: Dr Caroline Parkin cparkin@doctors.org.uk

SMJ 2009 54(1): 58

 

Introduction

Chiari malformations involve hindbrain herniation through the foramen magnum. They were classified by Professor Hans Chiari (1851-1916) into four types. Type I lesions (CIM) consist of caudal descent of cerebellar tonsils, without involving the brainstem. Type II lesions involve caudal descent of cerebellar vermis, forth ventricle, and lower brainstem. The term Arnold-Chiari malformation is specific to Type II malformations. The type III lesion consist a large sac of herniated cerebellum in the occipital region. The type IV lesion involves cerebellar hypoplasia.

 

Neurofibromatosis type one (NF-1) is a dominantly inherited syndrome due to a mutation in chromosome 17 (at17q 11.2). The condition is diagnosed when at least two of the seven criteria established by the National Institutes of Health Consensus Development Conference are met. These include: (1) six or more café-au-lait spots larger than 5 mm in the greatest diameter in prepubertal children and larger than 1.5 cm in postpubertal individuals, (2) two or more neurofibromas of any type or one or more plexiform neurofibroma, (3) freckling in the axilla or groin, (4) optic glioma, (5) two or more Lisch nodules, (6) a distinctive bony lesion such as sphenoid dysplasia bone or thinning of long bone cortex, (7) a first-degree relative with NF-11. In addition to these cardinal features NF-1 is associated with multiple abnormalities of the central nervous system2,3 and cardiovascular system including congenital heart disease, hypertension and vasculopathy4

 

This report describes the case of a patient with NF-1 and CIM. It aims to add to and summarise to the existing literature suggesting an association between the two conditions.

 

Case Report

A 31-year-old woman presented with a short history of shooting pains in both her arms and her right leg.  These pains were evoked by movement and any touch.  The pain was not responding to oramorph and gabapentin prescribed by her general practitioner.  She had no other symptoms of note; in particular no headache, limb weakness or sphincter disturbance.  She had been diagnosed with NF-1 4 years previously and had neuropathic pain in her left knee due to a neurofibroma which was surgically removed a year prior to admission.  The patient had a daughter with NF-1. The patient did not drink alcohol to excess or smoke. 

 

On examination she had stigmata of NF-1; café – au – lait spots, neurofibromata and Lisch nodules.  A full systems examination was normal. A neurological examination demonstrated mild weakness in the right upper limb (4+/5), a left sided foot drop due to previous knee surgery, brisk reflexes in the lower limbs and depressed reflexes in her right upper limb.  There was patchy loss of pin prick sensation in her upper limbs.

 

Routine blood tests, CXR and ECG were all normal.  An MRI of her brain and cervical spine demonstrated syringomyelia from C3 – C6 and platybasia with a CIM. She underwent decompression of her posterior fossa and made a good post-operative recovery. 

 

Discussion

Multiple reports have suggested CIM should be added to the list of dyplastic lesions associated with NF-1 2,5-7. Chakravarty et al8 suggested that a broadening of the diagnostic criteria for NF-1 is needed. They reported a patient with optic pathway glioma, scoliosis, CIM and syringomyelia, and questioned whether on the basis of these findings the patient could be diagnosed with NF-18.

 

Reports containing confounding data do however exist. There are three reports of patients with NF-1, hydrocephalus and CIM 5,9,10. It is difficult to discern in these cases whether CIM is the result of an embryonic defect shared with NF-1, or simply a consequence of hydrocephalus which predisposes to tonsillar ectopia. It may be that the hydrocephalus experienced by these patients is actually a consequence of displacement of the foramina of Magendi and Luschkae into the cervical canal obstructing CSF pathways.

 

Tubbs et al reported the first large series of patients with either condition11. They found that amongst 130 patients with CIM 5.4% had NF-1, and amongst 198 patients with NF-1 8.6% had CIM. The incidence of CIM in NF-1 was far greater than expected, suggesting a causal association rather than mere co-incidence. They hypothesized that the presumed mesodermal defect that results in a shallow posterior fossa is the same defect that leads to the genesis of NF-1. They also suggested that the formation of syringomyelia by CIM may be responsible for a proportion of the cases of scoliosis which is evident in approximately 10% of NF-1 patients12.

 

Awareness of the association of NF-1 with CIM promotes vigilance as to when symptoms experienced by patients with NF-1 necessitate further investigation. Hara and Arakawa7 described a patient with a history of recurrent periodic headaches, who had NF-1 and CIM. They highlighted that existing literature demonstrated that a recurrent periodic headache was the most commonly experienced symptoms by patients with both NF-1 and CIM and suggested that all NF-1 patients with recurrent periodical headache should undergo cranial neuroradiological studies. By identifying patients suitable for surgery, intervention to alleviate symptoms may be taken. Posterior fossa decompression is indicated in symptomatic patients21. The case reported here demonstrates that CIM in NF-1 can present with symptoms of syringomyelia rather than isolated headache, and hence is a further indication for imaging and surgical assessment in NF-1 patients.

  

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