Answers

Short answers

1 The epidural space.

2 The patient has extensive fat deposition in the epidural space, which results in encasement and effacement of the theca (fig 3 and fig 4); this probably causes compression of the terminal spinal cord and nerve roots.

View larger version (128K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3 Sagittal T1 weighted image of the lumbosacral spine showing effacement of the theca (arrowheads) by the extensive epidural lipomatosis (arrows)

 

View larger version (145K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 4 Sagittal T2 weighted image of the lumbosacral spine showing effacement of the theca (arrowheads) by the extensive epidural lipomatosis (arrows). Note the thin rim of cerebrospinal fluid (CSF) surrounding the spinal cord (upper arrowhead)

 

3 Spinal epidural lipomatosis.

Long answers
1 and 2 The abnormality
The spinal extradural space is extensively infiltrated with fat. There is pronounced effacement of the theca and cerebrospinal fluid, with encasement and circumferential moulding of the distal spinal cord, nerve roots, conus medullaris, and filum terminale. A thin rim of cerebrospinal fluid surrounds the spinal cord at the level of the upper arrowhead in fig 4. The axial T2 weighted images of the distal spinal cord (fig 5) and filum terminale at S1 levels (fig 6) show encasement of the theca, effacement of the cerebrospinal fluid signal, and narrowing of the exiting nerve roots by the extensive deposition of epidural fat in a "Y" configuration. The paraspinal muscles show pronounced fatty infiltration.

View larger version (146K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 5 Axial T2 weighted image of the distal spinal cord showing encasement of the theca (arrowheads), effacement of the cerebrospinal fluid signal, and narrowing of the exiting nerve roots (arrows) by the extensive epidural fat deposition in a "Y" configuration. Note the pronounced fatty infiltration of the paraspinal muscles (*)

 

View larger version (143K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 6 Axial T2 weighted image of the filum terminale at S1 showing encasement of the theca (arrowheads), effacement of the cerebrospinal fluid signal, and narrowing of the exiting nerve roots (arrows) by the extensive epidural fat deposition in a "Y" configuration. Note the pronounced fatty infiltration of the paraspinal muscles (*)

 
3 Diagnosis
Spinal epidural lipomatosis is a rare and complex disorder of progressive deposition of adipose tissue in the spinal epidural space that can present with progressive neurological deficits. Around 75% of those affected are young men, and the mean age at presentation is 43. The disorder may be idiopathic or associated with Cushing’s disease, hypothyroidism, pituitary prolactinoma, or obesity.^{1 2}

Hypertrophy of the epidural adipose tissue progressively narrows the spinal canal and compresses the neural elements. However, the severity of dural compression is not significantly associated with neurological complications.³ Back pain is the most common symptom, followed by slowly progressive weakness of the lower extremities and sensory changes with radicular symptoms. Bowel and bladder incontinence have been reported.⁴ The symptoms depend on the region of the spinal canal that is affected—myelopathic symptoms if the thoracic region is affected and radicular or cauda equina symptoms if the lumbar region is affected. Most patients (58-61%) have thoracic involvement, so progressive myelopathy is a more common presentation than radicular problems. Epidural lipomatosis of the cervical spine has never been reported.^{1 2}

Magnetic resonance imaging is the imaging modality of choice. Grading helps in the diagnosis and evaluation of spinal epidural lipomatosis, which in turn determine treatment and potentially the surgical approach. In patients with symptomatic disease, the sagittal epidural fat is more than 7 mm thick, and it forms a trifid configuration of the theca and neural structures—the "Y" configuration or sign.^{1 2 3 5}

Patients can be managed conservatively or by surgery. Patients treated conservatively should be weaned off steroids or encouraged to lose weight (15 kg or more),² both of which can reverse hypertrophy of the adipose tissue and relieve the neural compression. If conservative management fails, decompressive laminectomy and resection of epidural adipose tissue has some success. Patients with pathological conditions in the lumbar (cauda equina) region and those with idiopathic spinal epidural lipomatosis tend to have a better prognosis after surgical decompression but it is used only when conservative management fails.¹

Cite this as: BMJ 2009;338:a3183