Subcutaneous lipomas of the lumbar region consist of normal fat with variable amounts of connective tissue. It is this connective tissue component that distinguishes the lipoma from the surrounding subcutaneous fat as in this case. The variable connective tissue component decreases the signal intensity of the lipoma relative to normal fat on both the T1- and T2-weighted sequences. This departure from the normal appearance of fat also raises the differential consideration of a liposarcoma.
Lipomas of the lumbar region are frequently associated with dorsal dysraphism without meningocele (1). They may extend into the spinal canal (as in this case) and attach to the filum terminale or inferior aspect of the conus medullaris. None of these associations are seen in this case. Although there is no intradural extension of this lesion, lipomas can still cause neurological symptoms by virtue of their mass effect (2) and compression of the exiting nerve roots.
Patients with subcutaneous lipomas usually present in infancy or childhood. They may present later or may be picked up as an incidental finding. They can be seen with other anomalies, such as diastematomyelia, congenital dermal sinus or thickened filum terminale. Although CT is adequate for diagnosing the lipoma, MRI is preferred to evaluate intraspinal extent and position relative to cord and nerve roots, as well as to look for associated anomalies. Rarely, the lipomas can extend into the mediastinum and present as a chest mass (3). The main differential consideration is epidural lipomatosis which can be seen in patients on glucocorticoid therapy.