Multiple Bilateral Perineural Sleeve Cysts

A 51 year old male with low backache.  No neck pain. No radiating pain to any of upper limb.  No neuro deficit on clinical examination. No history of trauma.

Sagittal far lateral T2w section going through neural foramen of dorsal region spine show cystic signal intensity in the neural foramen with mild widening of corresponding neural foramen.  Sagittal and coronal MR Myelography image shows multiple bilateral cystic signal intensity along the nerve roots on either side of thecal sac.

Imaging wise : Bilateral Peri neural sleeve cysts.

In 1938 Tarlov first described cystic lesions of spinal nerve roots and introduced the term "perineural cyst". Perineural cyst (Tarlov’s cyst) is a cyst formation within the spinal nerve root sheath at the dorsal root ganglion. Most common in sacral region, may involve the cervical, thoracic or lumbar roots and are often multiple.
Associated with corresponding neural foraminal widening or focal scalloping of wall of bony spinal canal.
Exact mechanism not known. Trauma, hemorrhage and Arachnoid proliferation are the proposed mechanisms.  The primary pathology is a focal meningeal weakness resulting in dilatation of nerve root sleeves due to Csf pulsation and its hydrostatic pressure.
These are the leave alone lesions as they are often asymptomatic and detected incidentally. Usually associated with no neurological deficit, if any, may not correspond to cyst clinically.

Reference:  Multiple spinal nerve root cysts: Alparslan ~ENEL M.D. Orner Liitfi iyiGUN M.D. Zeki ~EKERCiM.D . Fahrettin ; Turkish Neurosurgery 2 : 41-43 1991

Tarlov cyst MRI

A 43 yo male with left side lower limb radiating pain.
MRI Lumbar spine : sagittal T2, axial T2 and MR Myelography images.

Findings:
A cystic lesion iso intense to Csf in sacral canal at the level of S2. Left traversing S2 nerve root seen separately in lateral recess with possible compression. An associated adjacent scalloping of bony walls of sacral canal.

Imaging wise diagnosis : Tarlov's cyst.

Tarlov's cyst.

Also known as Sacral Perineurial Cyst.
A Csf filled sac located in the spinal canal, formed within the nerve root sheath commonly found in sacral canal along the dorsal root ganglion. Occasionally in thoracic region.
Various hypotheses regarding the formation of these cyst are one is inflammation within the nerve root sheath followed by inoculation of fluids others are developmental or congenital origin, arachnoidal proliferation along the nerve root. Tendency of cyst to enlarge over a period of time is due to Csf being pushed into the cyst during systole pulsation but unable to get out of it - a ball valve like mechanism.

Usually asymptomatic, often detected incidentally during MRI. Cysts with diameters of over 2cm are more likely to be symptomatic due to compression over neighboring nerve roots. An associated adjacent bone erosion, neural foraminal or spinal canal expansion or scalloping is common.

The term Tarlov cysts often been misused or over used for referring to other cystic lesions in the sacral region. Tarlov cysts are often detected through MRI, but MRI cannot distinguish one major difference between Tarlov cysts and other cysts is the fact the walls contain nerve fibers. Therefore, the final diagnosis of a Tarlov cyst is not a radiological but rather a histopathological.