ACR Index: 3.1
LESION: Tarlov Cyst
ICD-9 code: 355.9
SYNOYM: Perineural cyst, Type II spinal meningeal cyst
DESCRIPTION: Tarlov or perineural cysts are cerebrospinal fluid-filled sacs usually located in the sacral spinal canal. The cyst occurs between the peri- and endoneurium of the spinal posterior nerve root sheath and is distinguished from other lesions by the presence of spinal nerve root fibers within the cyst wall, or the cyst cavity. They are often incidental findings on magnetic resonance imaging or computed tomography scans.
It is estimated that between 4.6% and 9% of the adult population has this cyst. Despite being initially described as asymptomatic, Tarlov cysts can produce symptoms in a small percentage of patients. They can distort or compress adjacent nerve roots producing symptoms which are now known to include coccygodynia, radicular pain, paresthesias, and bladder and bowel dysfunction, especially if the cyst diameter exceeds 1.5 cm. As a result, a perineural cyst(s) should be considered in the differential diagnosis of low back pain or lumbosacral radiculopathy.
PATHOGENESIS: Multiple theories have been proposed to explain the development of these cysts. These include:
2) hemorrhage into the subarachnoid space and subsequent degeneration of neural tissue,
3) congenital etiology,
4) dural lacerations during spinal surgery resulting in pseudomeningocele formation, and,
5) increased hydrostatic pressure of CSF. Presently, no consensus exits as to the mechanism of development. It is possible to cysts to enlarge over time due to hydrostatic and pulsatile forces.
COMMON LOCATIONS: Usually sacral, although cervical, thoracic, and lumbar Tarlov cysts have been described
GROSS MORPHOLOGY: These cysts are often multiple and extend around the circumference of nerves.
HISTOLOGY: Tarlov cyst outer wall is composed of vascular connective tissue, and the inner wall is lined with flattened arachnoid tissue. In addition, part of the lining containing nerve fibers also occasionally contains ganglion cells. Some cysts show evidence of hemorrhage.
Most patients will be asymptomatic, a small percentage will develop the following --
• Low back pain
• Radiculopathy (often at S2 and S3 nerve roots); Sciatica
• Cauda equine syndrome
• Pain – in hip, leg, foot, or perineal region; coccygodynia
• Bladder and bowel dysfunction – dysuria, urinary
• Sexual dysfunction
• Exacerbation of symptoms by standing, couphing,
• Sacral fractures (from erosion of sacrum)
• Angina like pain – if located in thoracic spine
Magnetic resonance imaging is preferred for initial imaging and will show a low signal on T1 and a high signal on T2 images consistent with CSF-characteristics. It can also show bone and pedicle erosion, sacral canal widening, and neural foramina widening.
If MRI cannot be performed, myelography is recommended since Tarlov cysts produce delayed filling, which distinguishes it from other spinal meningeal cysts. Post-myelography CT scanning with or without contrast is useful to detect perineural cysts (cysts appear isodense without contrast). CT can also show associated bony abnormalities including, cyst erosion of the sacrum, bone scalloping, and a rounded paravertebral shadow.
PROGNOSIS AND TREATMENT:
An asymptomatic cyst does not require treatment. Most cysts are static in size, however there is a potential for enlargement. For symptomatic cases, there is no consensus regarding optimal treatment.
•Non-surgical options: Patients are initially recommended to manage their symptoms with anti-inflammatory medications and physical therapy. Some patients may choose lumbar CSF drainage which can decrease hydrostatic pressure and therefore pressure in the cyst cavity. Percutaneous cyst drainage has been tried in some instances with fibrin glue replacement, however outcomes have been variable. Insertion of cyst-subarachnoid and cyst-peritoneal shunts have been attempted.