Disc herniation (disc prolapse) is displacement of the nucleus pulposus of the intervertebral disc through the annulus fibrosus into the posterior epidural space, neural foramen, or rarely the anterior space, due to degenerative or traumatic causes. In the lumbar spine, it most commonly occurs at L4-5 (45%) and L5-S1 (40%); in the cervical region, C5-6 and C6-7 are most frequently affected. Loss of nucleus pulposus hydration, annular tears, and mechanical loading predispose to herniation. Herniation types are anatomically classified into three categories: protrusion (disc material broad-based, not exceeding or partially exceeding outer annular fibers), extrusion (disc material narrow-necked extending beneath or above the posterior longitudinal ligament, wider than the base), and sequestration (disc fragment completely separated from parent disc, may show cranial or caudal migration). MRI is the gold standard: sagittal and axial T2-weighted sequences show disc material as hyperintense in the posterior epidural space; nerve root compression, degree of thecal sac compression, and herniation type are evaluated. CT myelography may be an alternative when MRI is contraindicated. Clinically presents with radiculopathy (dermatomal pain, sensory changes, motor weakness), low back pain, and rarely cauda equina syndrome (bilateral radiculopathy, bladder/bowel dysfunction, perineal anesthesia).
Age Range
20-60
Peak Age
40
Gender
Equal
Prevalence
Very Common
Disc degeneration begins with aging: the nucleus pulposus loses proteoglycan content → water retention capacity decreases → disc desiccation occurs → intradiscal pressure imbalance. The annulus fibrosus has a concentric lamellar structure and its weakest point is posterolateral (where the posterior longitudinal ligament is thinnest). Mechanical loading (axial compression + flexion + rotation) applies stress to degenerative annular fibers → radial tear develops → nucleus pulposus herniates through the path of least resistance (posterolateral). On MRI T2 imaging, herniated disc material appears hyperintense because the nucleus pulposus still contains water (high proton density, long T2 relaxation time) — brighter than the desiccated parent disc. Sequestered fragments may dehydrate over time and T2 signal decreases. On contrast MRI, neovascularization and inflammatory granulation tissue at the periphery of chronic herniation → rim enhancement is seen. This inflammatory response is actually the mechanism of spontaneous regression: macrophage infiltration phagocytoses the herniated fragment → size decreases. Nerve root compression causes radiculopathy through a combination of mechanical compression + chemical irritation (phospholipase A2, TNF-alpha, prostaglandins).
Hyperintense disc material extending beyond normal disc contour into the posterior epidural space on sagittal and axial T2-weighted MRI — pathognomonic finding of disc herniation. Herniation type (protrusion/extrusion/sequestration), size, direction, and nerve root relationship are evaluated based on this finding.
Hyperintense disc material is seen in the posterior epidural space on sagittal T2-weighted MRI. Material extending beyond normal disc contour may have similar or slightly different T2 signal intensity to the parent disc. Protrusion shows broad-based continuity with parent disc, extrusion shows narrow-necked connection, sequestration shows complete discontinuity. Cranial-caudal extent of disc material, degree of thecal sac compression, and nerve root relationship are evaluated on the sagittal plane.
Report Sentence
Hyperintense disc material extending into the posterior epidural space at the __ level on T2-weighted sequences, consistent with __[protrusion/extrusion/sequestration].
On axial T2-weighted MRI, herniated disc material displaces and compresses the nerve root. The normal nerve root sits freely in the neural foramen surrounded by epidural fat. In herniation, disc material pushes the nerve root posteriorly or laterally → root swells (edema), becomes compressed, and epidural fat is obliterated. The traversing root (going to the level below) is affected in posterolateral herniation, while the exiting root (leaving at that level) is affected in foraminal herniation. In far-lateral (extraforaminal) herniation, the exiting root is compressed.
Report Sentence
The __[left/right] __[L4/L5/S1] nerve root is displaced and compressed by herniated disc material; perineural edema signal is present.
On T1-weighted MRI, herniated disc material usually appears isointense to the parent disc — similar intermediate signal intensity to muscle and disc tissue. Epidural fat is hyperintense on T1, and in herniation this fat plane is obliterated → fat obliteration is evaluated as an indirect sign of disc herniation. Sequestered fragments may dehydrate over time and show slight signal change on T1. Hemorrhagic disc herniation may show T1 hyperintensity due to methemoglobin.
Report Sentence
Isointense structure to disc material in the posterior epidural space at __ level on T1-weighted sequences with obliteration of foraminal fat plane.
HIZ (High Intensity Zone) is a focal, high-signal (CSF-like) focus localized in the posterior annulus on T2-weighted sagittal MRI. It is the MRI correlate of annular fissure/tear. It reflects infiltration of water content from the nucleus pulposus posteriorly along the annular tear. HIZ presence correlates with discogenic pain — positive correlation with painful disc on provocative discography is 82-89%. Not all HIZ are symptomatic; prevalence in asymptomatic individuals is 24-33%.
Report Sentence
Focal hyperintense focus (HIZ) in the posterior annulus at __ level on sagittal T2, consistent with annular tear.
Thin rim enhancement around the periphery of chronic disc herniation is seen on contrast MRI. This enhancement reflects neovascularization of inflammatory granulation tissue developing around herniated disc material. Enhancement is usually absent or minimal in acute herniations. Presence of enhancement is critically important in differentiating postoperative scar tissue from residual/recurrent herniation: scar tissue shows homogeneous enhancement, while herniated disc shows peripheral rim enhancement.
Report Sentence
Thin peridiscal rim enhancement around herniated disc material at __ level on contrast MRI, suggesting chronic herniation.
Soft tissue density (50-80 HU) disc material is seen in the posterior epidural space on axial CT. It contrasts with normal epidural fat (approximately -100 HU). Calcified disc herniation may show very high density (>100 HU) and may be missed on MRI as T2 hypointense. CT better evaluates lateral recess narrowing, foramen invasion, and bony relationship on axial sections than MRI. Sagittal reformat images are critical for determining herniation type and level.
Report Sentence
Soft tissue density disc herniation at __ level in the posterior epidural space on axial CT with __[right/left] paramedian location.
Criteria
Broad-based disc material (>25% of disc circumference), convex posterior margin, partial annular integrity preserved
Distinct Features
Mildest form, nucleus has not yet fully exited annular fibers. Best prognosis, spontaneous regression common
Criteria
Narrow-necked disc material, wider than base in any plane, may have crossed posterior longitudinal ligament
Distinct Features
Causes more significant nerve root compression. Paradoxically, spontaneous regression is more common than protrusion — stronger inflammatory response against large fragment
Criteria
Disc fragment completely separated from parent disc, shows cranial or caudal migration, no continuity
Distinct Features
Migrated fragment may cause symptoms at a different level. Highest spontaneous regression rate (70%+) — free fragment exposed to immune system, active macrophage phagocytosis
Criteria
Disc material extends into neural foramen or extraforaminal region, affects exiting nerve root
Distinct Features
Different root affected than classic posterolateral herniation (exiting root). May be missed on axial MRI — sagittal and coronal planes critical. Surgical approach differs
Distinguishing Feature
Synovial cyst shows markedly hyperintense cystic morphology on T2 with continuity to facet joint and posterolateral location; disc herniation is solid/intermediate signal structure originating from disc level
Distinguishing Feature
Spinal stenosis shows multilevel canal narrowing with predominant ligamentum flavum/facet hypertrophy; disc herniation is usually single-level focal pathology
Distinguishing Feature
Degenerative disc disease shows dominant T2 signal loss, disc height loss, and Modic changes without herniation; disc herniation specifically refers to disc material extending beyond the canal
Urgency
urgentManagement
conservativeBiopsy
Not NeededFollow-up
6-month80-90% of disc herniations improve with conservative treatment in 6-12 weeks. Cauda equina syndrome (bilateral radiculopathy, bladder retention, perineal anesthesia) constitutes emergency surgical indication (<48 hours). Progressive motor deficit requires urgent surgery. Severe radiculopathy unresponsive to 6-12 weeks of conservative treatment is an indication for elective surgery (microdiscectomy). Sequestered fragments have the highest spontaneous regression rate (70%+).
Disc herniation is one of the most common causes of low back pain and radiculopathy. Most patients respond to conservative treatment (analgesics, physical therapy). Cauda equina syndrome (bilateral radiculopathy, bladder/bowel dysfunction) constitutes an emergency surgical indication. Surgery (microdiscectomy) is considered for progressive motor deficit or failure of conservative treatment.