Spinal Epidural Lipomatosis

Clinical History

A 40 year old man was evaluated for bilateral lower extremity diminished motor strength and function and persistent back pain for 2 months.

Imaging Findings

A 40 year old man was evaluated for bilateral lower extremity diminished motor strength and function and persistent back pain for 2 months.
The patient underwent bone marrow transplantation 3 years ago, with corticosteroids use for along period (medrol 48mg/day IV) due to chronic graft versus host disease (GVHD).
MRI examination was performed. A lack of signal with abnormal cutoff was demonstrated at MR myelography (Fig 1). The axial T2-weighted image at the L5/S1 level demonstrated the characteristic ‘Y-sign’ of the thecal sac (Fig 2a). The sagittal T2-weighted image showed an increase in epidural fat which was most obvious at the L4 to S1 levels (Fig 2b). The T1WI with fat suppression confirmed the presence of adipose tissue (Fig 3).

Discussion

Spinal epidural lipomatosis (SEL) is defined as pathological overgrowth of the normally presented extradural fat and often causes dural impingement. Symptomatic epidural lipomatosis was first described by Lee et al., in 1975 in a patient after renal transplantation. Subsequent reports on this rare clinical entity also implicated the administration of steroid as the major cause for SEL but a number of non–steroid-related cases have been reported, including some associated with Cushing disease, Cushing syndrome, hypothyroidism, pituitary prolactinoma, and obesity. Adipose tissue is usually found in the spinal epidural space. There is no essential histologic difference between the accumulated epidural fat and the normal epidural adipose tissue. However, an abnormal epidural fat overgrowth produces a clear conflict between the dural sac and the adipose tissue within the noncompliant space of the osseous spinal canal. Hence, SEL is a pathological condition caused by simple hypertrophy of unencapsulated mature adipocytes. The direct mechanical compression of the dural sac and vascular compromise contribute to the neurologic dysfunction in spinal epidural lipomatosis.
Back pain is the most frequently reported symptom associated with SEL and often presents long before the other symptoms. Lower-extremity weakness is also a common complaint and appears to be slowly progressive in most cases. Sensory changes with numbness, paresthesias, or radicular symptoms are also common. Bowel and bladder incontinence are reported, but appear to be rare complaints. On physical examination, lower-extremity weakness is the most common finding with decreased pinprick sensation and altered reflexes also frequently occurring.
Spinal MRI is the diagnostic imaging modality of choice. On conventional spin echo MRI, fat demonstrates high signal intensity on non-contrast T1-weighted images and intermediate signal intensity on T2- weighted images. On axial MRI of the lumbar spine, the thecal sac can have a stellate appearance with three rays radiating from the central core. This configuration was described by Kuhn et al as the ‘Y-sign’ of the thecal sac, a finding which is pathognomonic for lumbar epidural lipomatosis. The normal range for sagittal epidural fat thickness is approximately 3-6 mm, while in symptomatic spinal epidural lipomatosis, the sagittal epidural fat thickness may reach up to 7-15 mm.
Treatment options include conservative therapy and surgical intervention. Conservative therapy, including weaning of patients from steroids and weight loss, has been successful in a number of cases. Surgical intervention, with decompressive laminectomy and resection of epidural adipose tissue, has reportedly been successful in a large percentage of patients.

Differential Diagnosis List

Final Diagnosis

Spinal Epidural Lipomatosis

URL:	https://www.eurorad.org/case/7779
DOI:	10.1594/EURORAD/CASE.7779
ISSN:	1563-4086