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

Developmental Lesions and Tumor like masses

Epidural lipomatosis is excessive deposition of unencapsulated fat in the epidural space, most commonly in dorsal thoracic spine. It is typically associated with hypercortisolemia and is occasionally seen due to obesity, antiretroviral drugs or is idiopathic. Although it may be asymptomatic, patients usually present with weakness (72%); decreased sensation or reflexes (50%); and mild back pain. MRI images demonstrate homogeneous high signal intensity of epidural fat on T1-weighted images (Fig- 5) with suppression on STIR images.

Enlarged epidural veins are often seen in conjunction with vascular lesions such as arteriovenous malformations (Fig- 6a,b), fistulas (Fig- 7a,b), and varicose veins. In cases of major systemic venous thrombosis, the epidural veins could serve as collateral pathways. The other causes include herniated disc, abscess, tumor, hematoma, obesity, pregnancy, epidural lipomatosis and synovial cyst.⁵ Multiple lumbar epidural varices can cause nerve root and thecal sac compression.
MRI findings include normal or enlarged spinal cord in a dural AVM or AVF with intramedullary high signal and peripheral hypointensity (deoxyhemoglobin in pial capillaries) on T2W images. Prominent vessels are often found on the posterior aspect of the spinal cord. Associated subacute necrotizing myelopathy may be seen in the form of necrosis in the spinal cord. 

Extramedullary haemopoiesis (EH) is a compensatory process associated with chronic haemolytic anaemia like thalassaemia and myelodysplastic syndromes. It may rarely cause spinal cord compression. The EH masses are isointense epidural lesions on both T1- and T2-weighted images with intermediate enhancement on post contrast images (Fig- 8a,b). Associated marrow reconversion in the vertebral bodies and expansion of thoracic ribs with bilateral paravertebral masses are characteristic.⁹

Dural Ectasia is the enlargement of dural sac and nerve root sleeves, most often in lumbar and sacral regions. This results in scalloping of posterior vertebral bodies, widening of spinal canal and neural foramina with or without spinal cord and nerve root compression (Fig- 9a,b). Anterior and lateral meningoceles can be seen with dural ectasia. These can be incidental or may be seen with, neurofibromatosis, Marfan’s, Ehler Danlos syndromes and ankylosing spondylitis.