Most Common Causes of Sciatic Nerve Compression

The most common cause of sciatic nerve compression is lumbar disc herniation, particularly at the L4-L5 and L5-S1 levels. 1

Primary Causes of Sciatic Nerve Compression

Lumbar disc herniation: Herniation of the nucleus pulposus through its fibrous outer covering at L4-L5 and L5-S1 levels is the predominant cause of sciatic nerve compression 1
Spinal stenosis: Narrowing of the spinal canal causing bony constriction of the cauda equina and emerging nerve roots 1
Neoplasm: Tumors can compress the sciatic nerve or its nerve roots 1
Infection/inflammation: Inflammatory processes in the spine can lead to nerve compression 1
Hemorrhage: Bleeding around the nerve roots can cause compression 1

Piriformis syndrome: A non-discogenic cause where the sciatic nerve is compressed by the piriformis muscle as it passes through or around it 2
Vascular disorders: Large aneurysms, particularly those arising from iliac vessels, can compress the sciatic nerve 3
Trauma: Avulsion fractures (such as of the ischial tuberosity) and posterior hip dislocations can lead to sciatic nerve compression 4
Congenital anomalies: Structural abnormalities present from birth can affect the sciatic nerve pathway 4

Patients typically present with pain radiating down the leg below the knee in the distribution of the sciatic nerve 1, 5
Associated symptoms may include:
- Sensory impairment in the affected dermatomes 5
- Motor weakness in the distribution of affected nerve roots 5
- Diminished deep tendon reflexes 5
- Positive straight-leg-raise test (reproduction of sciatica when the leg is raised between 30-70 degrees) 1, 5

MRI is the imaging study of choice for evaluating suspected sciatic nerve compression due to its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and evaluate spinal canal patency 1, 5
CT scan can be useful when MRI is contraindicated and can determine if cauda equina compression is present (≥50% thecal sac effacement on CT predicts significant spinal stenosis) 1
CT myelography may be necessary for surgical planning or in patients with significant artifact from metallic surgical hardware on MRI 1

Pitfall: Focusing only on spinal causes can lead to missed diagnoses of extra-spinal causes such as piriformis syndrome or vascular disorders 2, 3
Pitfall: Delayed diagnosis of aneurysmal causes of sciatica can lead to poor prognosis 3
Pearl: Clear clinical identification of the affected nerve roots with corresponding pathological findings on imaging is the best predictor of successful surgical outcomes 6
Pearl: In patients with normal neurological examination and negative straight leg raising test results but persistent sciatica, consider piriformis syndrome 2

Sciatic neuropathy in children is uncommon and may have different etiologies than in adults 4
Females more commonly present with piriformis syndrome than males 7
Psychosocial stability is a positive predictive factor for surgical outcomes, while impaired fibrinolysis (occurring in smokers, sedentary individuals, and the obese) may be a negative predictive factor 6