Dorsal epidural disc migration

Dorsal epidural disc migration represents, as the name suggests, migration of disc material, usually a sequestrated disc fragment, into the dorsal (posterior) epidural space, posterior to the theca. This is a rare occurrence, often not suspected preoperatively and is almost invariably encountered in the lumbar region. 

Epidemiology

Although true epidemiological data is unavailable due to the small number reported and unknown number of undiagnosed cases, there appears to be a male predilection, and a tendency to affect middle to older individuals ¹. 

Clinical presentation

Clinical presentation is difficult if not impossible to distinguish from other causes of canal stenosis, such as anterior epidural disc herniations, synovial cysts or epidural haematomas. Patients typically present with cauda equina compression or radiculopathy ^1,3. 

Radiographic features

Dorsal epidural disc migration almost invariably is encountered in the lumbar region, typically L3/4 or L4/5 ¹. The disc material may be sequestrated (i.e. no communication with the disc space) or merely migrated, with additional material located lateral and anterior to the thecal sac ¹. 

MRI

MRI is the modality of choice for evaluating patients with canal stenosis and/or cord or/ cauda equina compression. The signal intensity of dorsally migrated disc material is similar to that seen elsewhere; in other words it is of variable signal intensity. Typical signal intensity is as follows ^1,2:

• T1
  • intermediate to low signal
• T2
  • intermediate to high signal
  • may have signal loss centrally if it contains gas
• T1 C+
  • peripheral enhancement
  • rarely solid enhancement is encountered

Treatment and prognosis

Treatment of dorsal epidural disc migration is largely surgical, with laminectomy and resection of the disc material. 

Differential diagnosis

• synovial cyst
• epidural abscess
• epidural haematoma