Friday 5 August 2011

Intraspinal mass, a nerve sheath tumor on MRI; Importance of MR Myelography

MRI Lumbar spine
Sagittal T2
Sagittal T1, Sag and Cor MR Myelogram
Axial T2 sections at the level of abnormality
A solitary well-demarcated ovoid solid mass caudal to conus medullaris.
Lesion is intra dural and extra medullary on MR Myelography. 
No question of compression over cord as lesion is caudal to conus. Nerve roots of caudal equina are splayed in thecal sac and compressed by the side of mass.
Size of the lesion ~28x11mm, hyperintense T2w images.
Lesion not broad based to dura, not extending out of neural foramen on axial T2w images.
No obvious bony canal remodeling.

Imaging wise DDs : An extramedullary Intradural lesion, Nerve sheath tumor possible. 
Meningioma unlikely as lesion is not broad based to dura and signals are hyperintense on T2 w images as not necessary but Menigoma are iso to hypo intense.

Histopathology: Nerve sheath tumor - Schwannoma.

Intra spinal masses

Mass lesions in spinal canal are classified as epidural, intradural and intramedullary.
Techniques for demonstration includes Xray Myelography, CT Myelography and MR Myelography. At present times MR Myelography is ideal and investigation of choice.
The different patterns on MR Myelography by which a lesion may be partly elucidated, whether it is intramedullary, intradural or epidural is as follow.
In above case, lesion is at the center of spinal canal, completely occupying the spinal canal with obliteration of Csf spaces, making an acute angle on either side on MR Myelo. The pattern resembles to B but it can not be intramedullary lesion as cord has already ended above the level of lesion. So its intradural and extramedullary. Above patterns are applicable only at the level of cord.

MR Myelography

Magnetic Resonance Myelography is studying the spinal canal and subarachnoid space by high-resolution MRI, a sequence in which strong T2 weighting is used to provide high contrast between the 'dark' spinal cord and the surrounding 'bright' Csf space.
MR myelography is an additional sequence, has become part of an entire MR examination and virtually replaced the traditional X-ray myelography which used contrast with radiation exposure. It was a procedure, to be done under aseptic precaution. Lumbar puncture was done first for intrathecal injection of iodinated contrast followed by x ray shoots in AP and Lateral view. Overall its was a time consuming procedure.
MR Myelo on the contrary requires no intrathecal contrast, its a T2 weighted fast spin echo pulse sequence. Due to its strong T2 weighting it uses its inherent contrast. No radiation exposure. No risk and complications of lumbar puncture. Its a Fast sequence it hardly takes couple of seconds. 

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