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Disc Bulge


KEY FACTS

Terminology

  • Anular bulge

  • Generalized extension of disc beyond edges of vertebral ring apophyses

Imaging

  • Circumferential disc “expansion” beyond confines of vertebral endplates

    • Short radius of extension: ≤ 3 mm

    • > 25% of disc circumference

    • If morphologic abnormality is < 25% of disc circumference, then it is herniation and not bulge

  • Smooth ventral extradural defect in contrast column, with indentation on anterior thecal sac

    • Central canal and subarticular recesses usually not compromised unless associated with ligamentous hypertrophy

  • T1WI and T2WI MR with sagittal and axial planes

  • Discography may help identify symptomatic disc

Top Differential Diagnoses

  • Disc protrusion (< 25% of disc circumference)

  • Ossification of posterior longitudinal ligament

    • Most common in cervical spine (70%)

  • Vertebral endplate bony spur

    • Continuous with vertebral endplate

Pathology

  • Bulge less important as separate entity but associated with disc degeneration and anular fissures → “discogenic” pain

Clinical Issues

  • Low back pain

  • Up to 39% of asymptomatic adults have bulging discs

  • > 80-90% success rate with conservative treatment

Axial T1WI MR shows the typical pattern of a lumbar broad-based vertebral disc bulge
at L5-S1. The disc extension beyond the vertebral body margin is diffuse, with no focal protrusion.

Axial T2WI FS MR in the same patient demonstrates the broad-based appearance of the bulging disc
with predominately low signal intensity. Associated anular fissure would show focal high signal.

Sagittal T2WI in a 39-year-old man with low back pain shows desiccation, loss of height of both L3-4
and 4-5
. Note indentation on the anterior aspect of the thecal sac at L3-4
caused by mild diffuse disc bulge at this level.

Axial T2WI through the L3-4 disc in the same case shows mild circumferential bulging of the disc
, seen here as smoothly rounded contour without any focal protrusion of disc material.

TERMINOLOGY

Synonyms

  • Anular bulge, annular bulge, bulging disc

Definitions

  • Generalized extension of disc beyond edges of vertebral ring apophyses

    • Greater than 25% of disc circumference

    • Typically extends less than 3 mm beyond edge of apophyses

IMAGING

General Features

  • Best diagnostic clue

    • Circumferential disc “expansion” beyond confines of vertebral endplates

  • Location

    • Cervical: C5-C6 and C6-C7 most common

    • Lumbar: L4-L5 and L5-S1 most common

  • Size

    • Short radius of extension: ≤ 3 mm

  • Morphology

    • Broad based

      • –

        > 25% of disc circumference

      • –

        If morphologic abnormality is < 25% of disc circumference, then it is a herniation and not a bulge

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