Surgical intervention for the asymptomatic lipoma of the conus medullaris has been an area of controversy,
The majority of authors propose early prophylactic untethering in patients with asymptomatic lipoma of the conus medullaris because of the low rate of neurological worsening (3-4%) resulting from the operation and because of the better neurological outcome at follow up of the asymptomatic patients as compared with that of symptomatic patients.
Diastematomyelia (SCM)
Diastematomyelia, also referred to as SCM, refers to the splitting of the spinal cord, conus medullaris, or terminal filum in the sagittal plane into two not necessarily equal halves.[26,56] A united theory of SCMs describes a Type I malformation as a split cord residing in a common dural tube and a Type II malformation as a split cord divided by a bone spur with each hemicord residing in a separate dural tube.[56] A thick cutaneous hairy patch usually overlies the region of the diastematomyelia. Diastematomyelia may account for up to 25% of OSD cases.Bone anomalies are present in 85% of cases, and scoliosis is present in 50% of cases of diastematomyelia In 91% of cases, the two hemicords reform a single cord below the site of division. In 50% of cases, the hemicords are contained within a single dural tube (Type I malformation; Figure 5) without a midline bone spur.Tethering may occur as a result of dorsal tethering bands between the hemicords and dura or from a thickened terminal filum. In the other 50% of cases, a median septum divides the hemicords, which are contained within separate dural tubes (Type II malformation). The median septum lies external to both dural tubes. Axial CT or CT myelography, or MR imaging (Figure 6) is useful in demonstrating the hemicords and median septum.[48] Surgical intervention may involve resecting the median septum and dividing a thickened filum and dorsal tethering bands. Andar, et al.,have suggested that, although surgical intervention in patients with diastematomyelia may stabilize progressive neurological and urological symptoms and may prevent the onset of neurological and urological deterioration, it may not affect the emergence of the neuroorthopedic syndrome of limb-length asymmetry and foot deformities.
Figure 5 (click image to zoom) . Intraoperative photograph showing a diastematomyelia (SCM).
Figure 6 (click image to zoom) . Axial MR images revealing a split spinal cord (diastematomyelia). The images are displayed in a cranial-to-caudal direction, left to right and top to bottom.
The Dermal Sinus
Dermal sinus tracts appear as midline dimples in the lumbosacral region
[26] and may extend from the skin surface to the dura, subarachnoid space or the spinal cord,[48] thereby causing tethering. The sinus tracts may serve as a pathway for infection and may present as meningitis.[48] The extraspinal course of the dermal sinus may be visualized by CT or MR imaging whereas the intraspinal course of the dermal sinus may be visualized with CT myelography or MR imaging (Figure 7).[48]
Figure 7 (click image to zoom) . Sagittal MR image revealing a dermal sinus tract (arrow) that extends from the skin and attaches to the spinal cord.
Tight Filum Terminale Syndrome
The tight filum terminale syndrome refers to the clinical presence of the TCS in a patient with a low-lying conus medullaris, a terminal filum greater than 2 mm in diameter and no other tethering agents. In 86% of the patients, the tip of the conus medullaris lies inferior to L-2.[13] The terminal filum is the tethering agent and these patients respond to sectioning of the terminal filum.[69,70] The low-lying conus and thickened terminal filum may be visualized on CT or MR imaging.
