Most are found in the lumbar spine of middle-aged and older adults but may occur at any age.

They are seen as small areas of high T2 signal in posterior band of anulus fibrosus.

Annular fissures may enhance after contrast administration (representing in-growth of granulation tissues).

They may be asymptomatic or produce symptoms by virtue of release of inflammatory substances that irritate nerve endings.

It is better to avoid using the term “tear” as it may have legal implications.

By 18 years of age, 28% of population has degenerative changes, and after 50 years of age, 85% to 95% have degenerative changes; low T2 signal intensity of discs probably reflects loss of proteoglycans.

Most lumbar herniated discs occur at L4-L5 and L5-S1 and are slightly eccentric in location due to median ligament.

Herniated disc implies a fissure in the anulus fibrosus (small linear area of high T2 signal) with posterior protrusion/extrusion of nucleus pulposus, which may be contained by an intact posterior longitudinal ligament (PLL) (subligamentous) or be accompanied by a tear of that ligament.

Central and slightly eccentric herniated discs affect the roots exiting at the level immediately below.

90% of individuals with disc herniations show clinical improvement after 8 to 10 weeks of symptomatic treatment, 50% show significant reduction in size of herniation by magnetic resonance imaging (MRI), and 8% to 10% will get worse. Improvement may be due to reduction of peridiscal hematoma and inflammatory changes.

Far lateral and extraforaminal disc herniations constitute 1% to 11% of all lumbar disc herniations and tend to occur more often in older (>50 years) male patients.

Most far lateral herniated discs occur at L2-L3 and L3-L4 levels.

Some lateral herniated discs occasionally produce bone erosion.

Recurrent or residual herniated discs may be a cause for the failed back syndrome.

A free disc fragment implies ruptured anulus fibrosus and PLL with migration of disc fragment.

Free disc fragments may migrate superiorly, inferiorly, bidirectionally, or posteriorly.

They may move into the lateral recess or posterior to the thecal sac and then become “sequestered.” Occasionally, they will erode the dura and become intradural.

Free disc fragments may be surrounded by granulation tissue, which enhances after contrast administration (especially on MRI).

Represent herniation of nucleus pulposus into the end-plate.

Most are found in the superior end-plate and are clinically asymptomatic or present with self-limiting back pain.

Most are found between T7-L2.

They may develop after an end-plate fracture.

They occur with equal frequency in the young and the elderly.

Schmorl nodes may show contrast enhancement acutely.

Occasionally, they may be large and “cyst-like.”

Main differential diagnosis: end-plate fracture, discitis, metastasis.

Cervical disc herniations may be symptomatic or asymptomatic; most occur during fourth to fifth decades of life; there is no prior history of trauma in most cases, but they may occur secondary to trauma.

By MRI, degenerative changes in the cervical spine are present in 25% of the population <40 years of age and in 60% of the population >60 years of age.

Most frequently involved levels are C5-C6 (30%) and C6-C7 (60%); most are central in location.

Axial T2 images creates white cerebrospinal fluid (CSF) and provides contrast with adjacent bone; T1 images may be done after administration of gadolinium (contrast is then created by enhancing the epidural plexus against black bone and CSF).

Occasionally, cervical herniated discs are bright on T1 images (hydrated calcium?).