Age / Sex : 62 / M

Age / Sex : 62/M

HIVD (disc sequestration)

Discussion

Findings:

 On T2-weighted image, there is a mass in the left epidural space at L4/5 disc level. The mass shows intermediate to low signal intensity on T2-weighted image.

After enhancement, the mass shows peripheral irregular enhacement.

Differential Diagnosis:

 Neurogenic tumor, Abscess, epidural fibrosis, Conjoined nerve root

Diagnosis:  HIVD (disc sequestration)

Discussion:

The term "sequestered intervertebral disc" is synonymous with the term "herniated disc with a free (detached) fragment." These terms define a herniation of nuclear material, through a defect in the annulus, that is no longer contiguous with the remaining parent disc. However, it is worthwhile to state that a herniated intervertebral disc may co-exist with a free detached fragment that has migrated upward or downward. The diagnosis of a sequestered disc is clinically important from the patient management standpoint. Indeed, sequestered discs may (a) produce misleading localizing signs and symptoms, (2) are contraindications to the use of percutaneous discectomy techniques, (3) are a known cause of postoperative back pain, and (4) require a more extensive surgical approach, preferably under sonographic control to ensure complete removal.

On T2-weighted images, free fragments appear oval in configuration. The differential diagnosis for MR findings of sequestered discs includes: (1) epidural abscess, distinguished from free disc fragments by the changes in the infected disc space and adjacent endplates, (2) extradural neoplasm, most commonly neurogenic tumor,  which usually T2-hyperinstensity. Neurogenic tumor shows usually strong homogeneous enhancement unless mass has cystic degeneration , (3) postoperative scar, which may have high T2 signal but which usually does not produce significant mass effect on the adjacent sac, and (4) postoperative fluid collections, which characteristically resolve spontaneously 4-6 weeks following surgery and usually are posterior rather than ventral to the sac.

Gadolinium may be used to enhance granulation tissue around the peripheral border of a free fragment. Contrast enhancement is useful for excluding diagnoses such as neurofibroma, epidural fibrosis, abscess, conjoined nerve roots, Tarlov cyst (dilated nerve root sleeve), calcified cyst of facet joint, etc. After Gd-DTPA administration, the

central portion of a free fragment of a sequestered disc maintains low signal intensity, whereas periphery is enhanced producing a Bull's eye sign.

References:

1. Birla R, Singh A, Kharat A, Phalke U. Role of contrast enhanced MR in diagnosis of a sequestered disc – a case report and review of literature. Ind J Radiol Imag 2005 15:4:489-491