Epidural Lipomatosis

Epidural lipomatosis (EL) is an uncommon but not a rare condition that frequently leads to spinal stenosis.

Pathophysiology

EL occurs due to excessive epidural accumulation of fatty tissue. It is most frequently encountered in the thoracic region, especially in the mid-thoracic section. Less commonly it is seen in the lower lumbar and sacral regions. In the thoracic region the fat usually accumulates posteriorly to the cord, whereas in the lumbar region it may be circumferential, surrounding the thecal sac.

The condition occurs in both genders, usually in the fourth or fifth decades. Most commonly it is found in patients on chronic exogenous steroid treatment, following epidural steroid injections, in patients with endocrine disorders that result in endogenous increased steroid production (Cushing's disease, hypothyroidism), in extremely obese individuals, and in HIV patients on protease inhibitors (which may cause lipodystrophy with central accumulation of fatty tissue). Not infrequently, idiopathic cases in healthy non-obese individuals are encountered.

Clinical Presentation

The most common symptoms include backache and, less frequently, radicular pain. Some patients present with intermittent claudication or unilateral radiculopathy simulating spinal stenosis or herniated disc, respectively. In patients with significant cord or thecal sac compression bilateral lower extremity weakness, reflex changes, sensory changes, and even urinary dysfunction may occur.

Imaging Studies

X-rays are usually negative. Osteoporosis and compression fractures may be seen in patients on long-term steroids. The CT scan will demonstrate low attenuation mass typical for the excessive, epidur-ally deposited, fatty tissue. In cases with severe thecal sac compression axial cuts will show a dural sac deformation in stellar, trifid, or Y shapes. This has been coined the Y sign and can also be seen on axial cuts in MRI examination. It has been proposed that the Y shape found in severe cases of epidural lipomatosis is brought about by the presence of meningovertebral ligaments that anchor the outer surface of the dura mater to the osteofibrous walls of the lumbar spinal canal.

MRI, the study of choice in these patients, will show a hyperin-tense soft tissue compressing the thecal sac on T1-weighted images. The cauda equina will clearly appear as dark crowded strands on the background of the hyperintense fatty tissue (Figures 4-22A and 4-22B). Fat suppression will change the signal to hypointense. On T2-weighted images the fat will appear with intermediate signal intensity.

The fatty tissue will not enhance after contrast administration. This helps in the differentiation of EL from tumors such as lymphoma.

Management

The management of patients with EL is determined by the etiology, the presenting symptoms, and the findings on clinical examina-

Crowding The Thecal Sac
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