In selected patients with depressed PTH levels, long-term withdrawal of vitamin D during HPN increases LSBMC and levels of PTH and 1,25(OH)2D. There is no reduction of the mean level of 25-hydroxyvitamin D.

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Neuropathy and glucose intolerance may occur despite increased serum chromium levels and respond to chromium infusion. The previous use of drugs such as metronidazole should not exclude chromium as a potential treatment for neuropathy in HPN patients.

A 47-year-old woman underwent elective surgery to resect a known intradural tumour at the T1 level. Histology confirmed the diagnosis of spinal meningioma. On follow-up, the patient was well and magnetic resonance (MR) imaging of the cervical spine was performed. What do the images show? What is the diagnosis? CMEArticle Clinics in diagnostic imaging (181)Wei 2a 2b 2c637 M e d i c a l E d u c a t i o n IMAGE INTERPRETATIONThe thin-walled structure (black arrows in Fig. 1) in the left neural exit canal at the C7-T1 level returns a low signal on the T1-weighted image (Fig. 1a), and a raised signal on the T2-weighted and turbo inversion recovery magnitude images (Figs. 1c & d, respectively). No enhancement is seen following contrast enhancement (Fig. 1b). The overall imaging features are in keeping with those of a cystic structure. On the axial T2-weighted images at the C7-T1 level, the left exiting C8 nerve root is detected on the cyst wall (white arrows in Figs. 2a & b). Findings are compatible with a left C8 transforaminal perineural cyst. Additional small perineural cysts are seen in the bilateral neural exit canals at the C6-7 level (white arrowheads in Fig. 2c). DIAGNOSISCervical spine perineural cysts. CLINICAL COURSEIn keeping with the most common presentation of perineural cysts, those found in the patient were asymptomatic and unlikely to be related to prior spinal surgery. They were incidentally detected and remained stable in size, morphology and signal intensities in subsequent surveillance MR imaging studies. DISCUSSIONMeningeal dilatation of the posterior spinal nerve root sheaths gives rise to perineural cysts, which contain cerebrospinal fluid (CSF) and nerve fibres. When occurring in the lumbosacral spine, they are colloquially known as Tarlov cysts, after Isadore Tarlov, who first described them during a cadaveric study of 30 specimens of filum terminale in 1938.(1) The aetiology of these lesions remains contentious. Some believe that they are congenital in nature, (2,3) while others proposed prior surgery, (2,4) haemorrhage (4) and increased CSF hydrostatic pressure as the possible pathogenesis. (2,5) It was estimated that 4.6%-9.0% of the adult population has perineural cysts.(5) They are most common in the lower lumbar and sacral segments, particularly the S2 and S3 nerve roots (Figs. 3 & 4).(6) Perineural cysts are often multiple and bilateral (Fig. 4).(1) They can be preforaminal, transforaminal or postforaminal in location -the latter being the least common location. On imaging, perineural cysts appear as circumscribed, thin-walled cystic lesions. Owing to their content, the cysts are isointense to CSF on all MR sequences. The demonstration of a traversing spinal nerve root through the cyst or along the cyst wall is a distinctive feature of perineural cysts (Figs. 4 & 5). (7) Diagnosis is more difficult in instances where the spinal nerve roots are at the periphery of the cyst wall (Fig. 6). When perineural cysts become large enough, they widen and remodel the neural exit canals or sacral ...