Features of spinal arachnoid cysts
These lesions represent intradural extramedullary fluid collections. They are most commonly located in the thoracic spine, where they form broad cavities partially divided by incomplete septa.
Due to the mass effect of the cyst, the spinal cord is displaced, lies closely against the anterior margin of the spinal canal, and may be flattened over areas of pronounced kyphosis. Prolonged compression leads to focal loss of spinal cord tissue volume and local myelomalacia (colliquative necrosis).
On MRI, cysts have a signal intensity identical to cerebrospinal fluid (CSF). However, on standard T2-weighted images (T2WI), specific artifacts may occur: CSF flow causes focal signal dropouts. To eliminate these distortions and clearly visualize the structure of the lesion, CISS (constructive interference in steady state) sequences are used.
Perineural arachnoid cysts (Tarlov cysts)
Tarlov cysts (Tarlov cysts) are a distinct variant of arachnoid cysts that have a specific localization.
- Location: Sacrum, predominantly at the level of the S2 nerve root.
- Morphology: Frequently large and multiple.
- Bone changes: Can cause eccentric erosion of the sacral canal due to constant fluid pressure.
Despite the fact that such cysts are well visualized on MRI and can reach impressive sizes, destroying bone tissue, their clinical significance remains questionable.
Syringomyelia: pathogenesis and causes
Syringomyelia (Syringomyelia) is a condition accompanied by the formation of a fluid-filled cavity (syrinx) within the spinal cord, lined by glial tissue and filled with fluid similar to CSF. The cavities form under the action of hydrodynamic forces that literally pump fluid into healthy neural tissue.
In 70–90% of cases, the pathology is associated with cerebellar tonsillar ectopia (descending tonsils down to the C1–C2 level). The main hypothesis for development in such cases (so-called syringohydromyelia):
- Intermittent obstruction of CSF flow through the foramen magnum and the outlets of the fourth ventricle occurs.
- An open communication between the fourth ventricle and the central canal of the spinal cord is maintained.
- Periodic distension of the central canal leads to secondary degeneration of the spinal cord tissue.
Other causes of cavity formation (cavitation) include intramedullary tumors, spinal trauma, and inflammation. They cause myelomalacia, which then organizes into cavities extending into normal tissue. In 10–20% of cases, the cause cannot be identified.
Morphology and diagnosis of syringomyelia
Typically, syringomyelia affects multiple cervical segments (less commonly just the thoracic) or the entire spinal cord. Small isolated fusiform cavities (fusiform syrinx) are less common. Less than 10% of cysts extend cranially above the C2 level.
Spinal cord dimensions vary as follows:
- Enlarged in ~80% of cases.
- Normal in 10% of cases.
- Diffusely atrophic in 10% of cases.
Spinal cord size may fluctuate depending on respiration and posture, but this does not correlate with the patient's clinical status.
MRI findings: A well-defined cavity with CSF signal on T1WI and T2WI is visualized. In pulsatile cysts, signal changes are noticeable due to fluid motion. Dynamic MRI (phase-contrast methods) is used for a detailed assessment of CSF dynamics.
Clinical correlation: There is only a moderate correlation between the presence/location of the cavity and symptoms. At the same time, there is no correlation between cyst size (or degree of distension) and the severity of patient disability.
Class and exam questions
Why can spinal cysts appear heterogeneous on standard T2WI?
Due to CSF flow artifacts, which manifest as focal signal dropouts. Special pulse sequences, such as CISS, are used to eliminate them.
Does the severity of syringomyelia symptoms depend on the size of the cystic cavity?
No, there is no direct relationship. Cyst size, the degree of central canal distension, and cavity size fluctuations do not correlate with the severity of clinical manifestations and disability.
Where are perineural Tarlov cysts most commonly located?
They are typically located in the sacral spine, predominantly at the S2 root level, and can cause local bone erosion.
What else to study on this topic
- MRI sequences suppressing CSF flow artifacts (CISS, FIESTA)
- Phase-contrast MRI in evaluating cerebrospinal fluid dynamics
- Cerebellar tonsillar ectopia (Chiari malformation) and its types
- Differential diagnosis of primary and secondary spinal cord cavitation
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Spinal arachnoid cysts" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Other topics in the "Spine" section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.