Neuroradiology Case of the Week

Case 34

Francisco Garcia-Morales, MD, José A Echeverri, MD, Manoj Ketkar, MD,
and Henry Z. Wang, MD, PhD

Clinical Presentation: Patient is a 33-year-old white female presenting with severe low back pain, left leg radiculopathy, and worsening urinary incontinence over the last 4 weeks. A recent CT from an outside institution showed spina bifida occulta. She was referred for a CT-myelogram to assess for tethered-cord. An MR was contraindicated due to past medical history of idiopathic hypertrophic subaortic stenosis and implanted intracardiac defibrillator in August 1997.

Radiological Findings: Conventional myelogram (Fig. 1) and lumbar Myelo-CT sagittal (Fig. 2) and coronal (Fig. 3) reconstruction images delineate a lobulated mass, with low attenuation (–120 HU) of the distal 6 centimeters of the spinal cord involving the conus medullaris, which ended at upper aspect of L2. The filum terminale had a normal appearance with no evidence of lipoma or tethering, measuring 2mm at the level of L5-S1. Incidental finding of a Tarlov cyst is noted.
   Axial Image (Fig. 4) show the intramedullary location and a septated appearance.

Figure 1: Lumbar myelogram showing the intramedullary lobulated mass as negative defects (arrows).	Figure 2: A CT-myelogram sagittal 2D reconstructed image shows the expanding intraspinal low-density mass (arrow) surrounding by myelogram contrast.
Figure 3: A CT-myelogram coronal 2D reconstructed image shows the intraspinal lipoma (arrows). Note the displaced nerve roots to the left of the conus. A Tarlov cyst (nerve root sleeve cyst or diverticulum) of left S3 is incidentally noted (arrowhead).	Figure 4: The intraspinal lipoma is noted with some septation (arrow). Note that there is no evidence of spinal dysraphism.

Diagnosis: Intramedullary lipoma.

Discussion:
   Spinal cord lipomas are rare tumors with a reported incidence of 1% of spinal tumors [1]. Intramedullary lipomas without dural or extradural extension are even rarer, with an incidence of 0.4 to 0.6% [2]. These lesions are usually not associated with dysraphism [3]. They are believed to result from premature disjunction of the cutaneus ectoderm from the forming neural tube [4].
   The neurological abnormalities depend on tumor size and location. Neurological symptoms may worsen after rapid weight gain or steroidal therapy [5]. It is believed that acute compression symptoms do not occur due to pliability of the lipomas. Intraspinal lipoma cells have the same metabolic properties as normal adypocytes suggesting that they are not lipomatous tumors but hamartomatous lesions, capable of growth and regeneration and can be influenced by diet and weight.
   MR is the modality of choice to diagnose intraspinal tumors due to its inherent tissue characterization, anatomical detail, and multiplanar capabilities. However, CT and particularly CT-myelography have proven to be important in the evaluation of intraspinal tumors, and are also excellent to characterize fatty tumors due to its low-attenuation values. CT is a valuable alternative when MRI is contraindicated as in this patient with intracardiac defibrillator.
   Treatment of these tumors is controversial but it is believed that they should be observed when found incidentally in asymptomatic patients. Patients with worsening neurological symptoms could benefit form decompressive surgery [6].

References:

1. Rogers HM, Long DM, Chou SN, French LA. Lipomas of the spinal cord and cauda equina. J Neurosurgery 1987; 34:349-354.
2. McCormick PC, Stein BM. Intramedullary tumors in adults. Neurosurgical Clinics of North America 1990; 1:609-630.
3. Fujiwara F, Tamaki N, Nagashima T, Nakamura M. Intradural spinal lipomas not associated with spinal dysraphism: a report of four cases. Neurosurgery 1995; 37:1212-1215.
4. McClone DG, Mutluer S, Naidich TP. Lipomeningoceles of the conus medullaris. Concep Pediatric Neurosurgery 1982;3:170-177.
5. McGillucuddy GT, Shucart W, Kwan ESK. Intradural spinal lipomas. Neurosurgery 1987;21:343-346.
6. Gazzaz M, Derraz S, Elouahabi A, et al. Intramedullary lipoma without spinal dysraphism: report of four cases. Panarab Neurosurgery Journal, Apr, 2001, pp1-6.