Pathophysiology and causes
The reduction of the reserve space for neural structures leads to increased cerebrospinal fluid pressure. This disrupts venous drainage, causes perineural congestion, and subsequent ischemia of the nerve fibers. The specific vascular anatomy makes the cauda equina roots (cauda equina) extremely vulnerable to ischemia, especially when the canal is narrowed at more than one level.
On contrast-enhanced MRI, roots may enhance due to the breakdown of the blood–nerve barrier and local inflammation. An interesting imaging marker of severe compression is the redundant nerve roots phenomenon (redundant nerve roots). In this case, proximal to the narrowing, the roots become thickened, elongated, and tortuous.
The main causes of stenosis development are facet joint osteoarthritis (especially in the lumbar spine), as well as hypertrophy and calcification of the posterior ligamentous apparatus (e.g., ligamentum flavum).
Clinical presentation
The condition can remain asymptomatic for a long time until an acute triggering event occurs. The pathognomonic syndrome is neurogenic intermittent claudication. It manifests with motor and sensory deficits, as well as severe leg pain during walking or prolonged standing.
A key feature of the syndrome is significant relief or complete disappearance of symptoms when leaning the torso forward or lying supine. This occurs due to a physical increase in the cross-sectional area of the spinal canal.
The pathology must be differentiated from vascular intermittent claudication and degenerative diseases of the hip or knee joints. A neurogenic bladder may develop as a serious complication (due to mechanical compression of the S2–S4 roots).
Imaging criteria (MRI)
MRI is the primary imaging modality, although a standard supine scan does not always reflect the full picture (unlike upright MRI with axial loading). The main MRI criterion for stenosis is the absence of the perimedullary cerebrospinal fluid space at the level of narrowing.
Cervical spine (C4–C7):
- Normal anteroposterior diameter: 17 mm.
- Critical stenosis value: less than 14 mm (with an average spinal cord diameter of about 7 mm).
Lumbar spine (Benoist classification):
- Mild stenosis: 12–14 mm.
- Moderate stenosis: 10–12 mm.
- Severe stenosis: less than 10 mm.
Foraminal stenosis
An important variant of acquired narrowing is foraminal stenosis. Normally, the intervertebral foramen has a teardrop shape with a height of 19–21 mm and a sagittal diameter of 7–8 mm. Disc bulging, focal osteophytes, or facet joint subluxation cause lateral compression of the nerve root.
The Wildermuth scale is used to assess the severity of foraminal stenosis:
- Grade 0: Normal. Foraminal epidural fat completely surrounds the exiting nerve root.
- Grade 1: Mild stenosis. Epidural fat is deformed but still surrounds the root.
- Grade 2: Moderate stenosis. The root is only partially surrounded by fat.
- Grade 3: Advanced stenosis. Complete obliteration (absence) of epidural fat.
Adult degenerative scoliosis
Stenosis often develops against the background of degenerative scoliosis—a deformity with a Cobb angle of more than 10 degrees in the frontal plane. Aebi classification identifies three types of adult scoliosis:
- Type I (Primary degenerative): develops in adulthood in the lumbar spine due to asymmetric disc and joint degeneration and fractures.
- Type II (Progressive idiopathic deformity): forms before skeletal maturity but begins to cause symptoms in adults.
- Type III (Secondary degenerative): arises due to pelvic tilt, hip pathology, or lumbosacral transitional anomalies.
Briefly: answers to topical questions
How does neurogenic intermittent claudication clinically differ from vascular claudication?
Neurogenic and vascular intermittent claudication differ in the dependence of symptoms on body position and physical activity, as well as pain localization and objective data.
| Sign | Neurogenic claudication | Vascular claudication |
|---|---|---|
| Dependence on exertion | Less dependent on the duration of activity | Has a "dose-dependent" character, occurs during movement |
| Pain relief | Relieved by leaning forward (spine flexion) | Alleviated at rest |
| Localization | Proximal (in the buttocks and posterior thigh) | Pain crescendo/decrescendo pattern |
| Physical examination | Normal skin color and temperature, pulses preserved | (No complete data in source) |
Which anatomical structures form the walls of the intervertebral foramen?
Sources do not contain a complete description of all walls of the intervertebral foramen. They indicate that:
- the length of the pedicle affects the width of the foramen;
- fusion of the ligamentum flavum with the facet joint capsule forms the border of the intervertebral foramen;
- enlarged superior articular process and focal osteophytes can cause nerve compression within the foramen;
- narrowing of the intervertebral disc significantly reduces the height of the foramen.
What conservative and surgical treatments are used for spinal stenosis?
Surgical treatment of spinal stenosis includes:
- Laminectomy (laminectomy) — removal of the vertebral lamina.
- Laminotomy (laminotomy) — removal of a small portion of the vertebral lamina.
- Foraminotomy (foraminotomy) — decompression at the level of the intervertebral foramen.
- Extended decompression — resection of articular processes (facet joints); absence of facet joints requires supplementing the surgery with spinal fusion for stabilization.
- Interspinous distraction (interspinous distraction) — placement of an implant between the spinous processes.
- Spinal fusion (fusion) is spinal stabilization.
For juxtafacet and synovial cysts, conservative and minimally invasive methods are used: percutaneous injections of local anesthetics and/or prolonged-action steroids; in case of concomitant stenosis, cyst excision, decompression, and laminectomy are performed.
How to remember the biomechanics of neurogenic claudication: trunk flexion mechanically "expands" the spinal canal and increases its cross-sectional area — the nerve roots get more space, ischemia decreases, and pain subsides. Spinal extension and standing upright, conversely, narrow the canal.
Class and exam questions
What is the «redundant nerve roots» phenomenon?
This is an MRI sign in which the cauda equina nerve roots, located proximally (above) the severe stenosis zone, appear thickened, elongated, and tortuous.
How to differentiate neurogenic claudication from vascular claudication?
In neurogenic claudication, pain occurs in the upright position and during walking, but quickly resolves with forward trunk flexion or in the supine position, as this reduces pressure on the nerve roots.
What is assessed using the Wildermuth scale?
Degree of degenerative foraminal stenosis. The 0 to 3 scale is based on how well the epidural fat around the nerve root is preserved or completely obliterated.
What else to study on this topic
- Clinical MRI examples of facet joint synovial cysts
- Secondary myelopathy in thoracic spinal stenosis
- Biomechanics of compression in spondylolisthesis (isthmic and degenerative)
- MR myelography and evaluation of residual redundant nerve roots following laminectomy
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