What is an intradural spinal cyst?

  Intraspinal spinal cysts originate from the spinal cord tegument and have an unclear etiology. The commonly accepted etiology is either a congenital dural diverticulum or an arachnoid herniation due to a congenital dural defect. Intraspinal spinal cysts are not uncommon, and since the widespread use of MRI in clinical practice, the detection rate can reach 4.6%, with 20% of patients presenting with symptoms of cyst compression, with the majority of spinal cysts occurring in the sacral spinal canal, while those occurring in the thoracolumbar segment are rare.  Classification of spinal cysts: Nabors and other classifications are currently used to classify intradural spinal cysts into 3 types: Nabors type I is an epidural spinal cyst that does not contain spinal nerve root fibers and includes two subtypes, type IA “epidural spinal cyst”, which often occurs in the lower and middle thoracic spinal cord dorsal to the spinal cord and is a solitary lesion. Type IB “sacral spinal bulge”, located mostly in S1-3, is often multiple.  Nabors type II is a spinal cyst containing spinal nerve root fibers, a spinal cyst containing nerve roots, also known as “Tarlov’s nerve bundle cyst”, usually located in the sacral canal, and may also involve cervical, thoracic or lumbar nerve roots.  Nabors III, an intradural spinal cyst, is located in the dural sac and can occur in the thoracic segment of the spinal cord, as well as in the cervical or lumbar segments. Spinal cysts that occur in the sacral canal are collectively referred to as sacral cysts, including Nabors IB and Tarlov cysts of Nabors II. The indications and surgical procedures for sacral cysts are still controversial, but microscopic resection of the cyst wall and repair of the CSF leak is still the most reliable procedure.  Long-segment epidural spinal cysts in the thoracolumbar segment, belonging to Nabors type IA, have intermittent, pulsatile compression of the spinal cord and cauda equina by its internal cystic fluid because the cyst is located on the dorsal side of the spinal capsule, and the compression gradually increases with the gradual rise of the cystic internal pressure. MRI is the preferred method of examination for intraspinal spinal cysts, which are in the form of long, striped pouches. The signal of the cyst is similar to that of cerebrospinal fluid, with low signal on Tl-weighted images and high signal on T2-weighted images, and no enhancement of the cyst wall. It is important to note that the close relationship between the cyst wall and the normal dura sometimes leads to a missed diagnosis. The characteristics of this disease are as follows: 1) long duration of intravertebral spinal cyst with fluctuating progression of symptoms and intermediate remission periods; 2) clinical manifestations are mainly chronic low back pain, bilateral lower limb weakness and dysfunction; 3) MRl has its characteristic manifestations, showing a well-defined long strip of cystic pouch shadow, located on the dorsal side of the spinal cord, with a thin band of low signal separating the cyst from the spinal cord and a homogeneous signal of the cystic fluid, which is the same as the signal of cerebrospinal fluid .  The epidural fat disappears and accumulates at the upper and lower ends of the cyst, showing arcuate or cup-like changes, suggesting that the cyst is located outside the dura. The local vertebral canal is widened, and the spinal cord is compressed, atrophied and thinned, and close to the posterior edge of the vertebral body. There is no enhancement of the cyst wall and cyst fluid on the enhancement scan. Due to its characteristic MR presentation, it is generally not necessary to differentiate it from other lesions.  For those who get a confirmed diagnosis of spinal cyst with typical clinical symptoms that affect the patient’s work and life or even neurological deficit, surgery can be performed in order to relieve the compression of the neural tissue. Dural defect is the key factor in epidural spinal cysts, and cyst excision and dural defect repair are the preferred surgical methods. After surgery, patients are instructed to lie prone for 5-7 days to ensure fistula healing. With reasonable treatment, the outcome is satisfactory and the recurrence rate is extremely low.