Fifth ventricle: an unusual cystic lesion of the conus medullaris.

STUDY DESIGN: Cystic dilatation of the fifth ventricle on its own is an extremely rare pathological event in adults whose pathogenesis is uncertain. The authors describe a personal case of 'fifth ventricle' and review the pertinent literature. OBJECTIVE: To emphasize the importance of including the fifth ventricle in differential diagnosis of lesions of the conus medullaris to ensure proper treatment. SETTING: Italy. METHODS: A 30-year-old woman was referred to us for recurrent low back pain. The patient was assessed by clinical, electrophysiological (motor evoked potential, somatosensorial evoked potential and electromyography of the perineal and lower limb muscles) and urodynamic investigations as well as a magnetic resonance imaging (MRI) of the lumbar-sacral segment with and without gadolinium enhancement, subsequently extended to the entire vertebral column and brain. Follow-up consisted of periodic clinical evaluation and lumbar-sacral MRI after 1 and 2 years. RESULTS: General physical examination, electrophysiological and urodynamic investigations were all negative, confirming the subjective nature of the patient's symptoms. Lumbar-sacral MRI demonstrated the presence of a cyst lesion containing cerebrospinal fluid (CSF), which did not enhance after gadolinium, compatible with the diagnosis of the terminal ventricle. By extending the MRI investigation to the entire vertebral column and brain, it was possible to exclude an association with other malformations of the central nervous system. Clinical and radiological follow-up confirmed the nonevolutive nature of the lesion 1 and 2 years later. CONCLUSIONS: The lack of clinical symptoms and the stability of the radiological situation at 1 and 2 years follow-up motivated our choice of conservative treatment.