Spinal Epidural Space:
Anatomy, Normal variations, and Pathological Lesions
on MR Imaging

Chhabra A, MD¹; Batra K, MD¹; Satti S, MD¹; Patel S, MMS¹; Feitell S, MMS¹; Gonzales C, MD¹; Faerber E, MD²; Koenigsberg RA, DO FAOCR¹

¹Drexel University College of Medicine, Philadelphia, PA
² St Christopher Hospital for Children, Philadelphia, PA

Degenerative Lesions

Degenerative changes in the spine which may cause impingement on the epidural space (ES) include, herniated disc, posterior osteophytes, ligament calcification, spondylolisthesis, facet joint arthropathy with or without synovial cyst.
Disc disc herniation(DDD) usually results in compression of the anterior epidural space, with lateral or medial irritation of nerve root or cauda equina (Fig- 13a, b). Rare locations are a foraminal position or dislocation dorsally¹². Sequestrated and extruded fragments usually show low signal on T1-weighted images and 80% give high signal on T2-weighted images. Most show peripheral contrast enhancement, attributed to an inflammatory response with granulation tissue. Ligamentous ossification involving posterior longitudinal ligament or ligamentum flavum is usually associated with decreased signal intensity on all sequences and may be difficult to distinguish from ligamentous hypertrophy (Fig- 14a,b), but there may be increased signal intensity on T1-weighted images because of marrow fat. Epidural masses may be simulated by hypertrophy of the posterior elements or by synovial cysts arising from the degenerated facet joints and projecting into the spinal canal or into the neuroforamina (Fig- 15a,b). Gout and Dialysis spondylitis are rare in the spine and are ususally centered over the intervertebral disc.¹³ Laminectomy and discectomy performed in the management of symptomatic lumbar disc herniation can also cause epidural lesions like, recurrent/residual disc herniation, epidural scar formation (Fig- 16a,b), pseudo-meningocele and abscess formation. Recurrent disc can be differentiated from scar by, hypointensity on T2W images, presence of mass effect and peripheral or no enhancement in immediate post contrast images.¹⁴ Pseudomeningocele may be seen as nonenhancing CSF intensity fluid collection with or without apparent dural communication. Presence of intermediate signal changes on T1W and peripheral enhancement on postcontrast images suggests presence of abscess.