2021 NPA-06

This case was originally published in 2021. The information provided in this case was accurate and correct at the time of initial program release. Any changes in terminology since the time of initial publication may not be reflected in this case.

A three-year-old girl was noted to have a large soft tissue mass in the midline lower lumbosacral region at the time of adoption. Neurologic function appeared normal. Lumbar spine MRI (Image A) showed an intraspinal, tethering, fibrofatty mass associated with sacral dysraphism. The spinal cord was tethered to the S2 level, and the intraspinal mass was contiguous with a midline fibrofatty subcutaneous back mass. No spinal cord syrinx was identified. She underwent an L5 laminectomy and resection of the mass.

Tissue Site
Lumbosacral spinal cord

H&E-stained slide of the lumbosacral spinal cord mass resection specimen.

There was no bony covering over the sacral spinal canal, and intraoperative ultrasound showed the intraspinal mass ended around the L4-L5 interspace. The subcutaneous and extradural fibrofatty mass was well-circumscribed and traced to a large entrance into the sacral spinal canal where it entered the conus medullaris and cauda equina of the spinal cord. Histologically, the mass was comprised of sheets of adipocytes separated by thin fibrovascular septa (Image B and Image C). Scattered embedded small nerve bundles (Image D) were present. The adipocytes were well-differentiated and mature without mitoses or significant nuclear atypia (Image E), consistent with a diagnosis of lipoma.

The lipoma in this case was associated with sacral spinal dysraphism. The neurosurgeon noted that the spinal cord was rotated with the anterior midline turned leftward and the caudal nerve roots all directed upwards. The lumbosacral spinal cord was also tethered at the S2 level. Tethered cord syndrome (TCS) is a neurologic disorder caused by traction on the conus medullaris, the terminal tapered end of the spinal cord that is normally found above the level of the L2 vertebral body; it is associated with reduced blood flow to the caudal spinal cord. TCS may cause lower back or leg pain, somatosensory changes such as numbness or tingling, bladder or bowel incontinence, and gait disturbances. Clinical presentation of TCS is dependent on the anatomic level at which the conus medullaris is found below the L2 vertebral body and differs between pediatric and adult patients; children are more likely to present with urinary bladder dysfunction, while adults are more likely to present with pain. Other symptoms may include paresthesias, bowel dysfunction, and motor deficits. Diagnosis of TCS is suggested with radiologic evidence of a low-lying conus medullaris below the L2 level and/or a filum terminale diameter greater than 2 mm in a patient with appropriate neurologic signs/symptoms.

TCS is most commonly associated with spinal dysraphism and attachment of the filum terminale to the dura mater or skin. Up to one-fourth of patients with TCS may also have syringomyelia. Spinal dysraphism refers to a spectrum of malformations ranging from occult spina bifida to open defects with herniation of leptomeninges and/or the spinal cord proper through the opening (eg, myelomeningocele). Closed spinal dysraphism categorically includes entities such as occult spina bifida, diastematomyelia, and lipomyelomeningocele; the latter is defined as a sacral or lumbar subcutaneous lipoma that is contiguous with an intradural lipoma, as seen in this case. Nondysraphic intradural lipomas are exceedingly rare. Closed spinal dysraphism is commonly associated with cutaneous findings such as sacral dimples, hairy nevi, and subcutaneous masses. Folic acid deficiency during gestation is linked to increased risk for spinal dysraphism, as are some antiepileptic drugs.

Primary neurulation normally begins with proliferation of the neuroectoderm to form the neural plate. Invagination of the neural plate and deepening of the neural groove approximates the neural folds and is followed by bidirectional closure of the tube beginning in the dorsal region around day 22 of gestation, terminating with closure of the rostral and caudal neuropores around days 24 and 26, respectively. Secondary neurulation occurs thereafter and is the process by which the caudal spinal cord is formed. Primitive neural stem cells that make up the caudal cell mass distal to the caudal neuropore become vacuolated, coalesce, canalize, and then connect to the central canal that was formed by primary neurulation to become the conus medullaris, filum terminale, and cauda equina. The conus medullaris is comprised of sacral and coccygeal neural tissue, while the filum terminale forms from pia mater and connects to the coccyx. As gestational development continues, the spinal column grows at a faster rate than the spinal cord resulting in ascent of the conus medullaris to above the level of the L2 vertebral body and elongation of the filum terminale and nerve roots to form the cauda equina. Ascension of the conus medullaris is typically complete by birth or within a few weeks thereafter. Spinal dysraphism occurs with defective formation or closure of the neural tube.

The presence of tethered cord may be asymptomatic or may reveal itself clinically in adulthood with a superimposed lumbosacral spinal injury or degenerative disease. Conservative watch-and-wait monitoring may be appropriate for asymptomatic adult patients, but because TCS can result in progressive neurologic dysfunction if left untreated, surgical detethering can prevent and/or alleviate symptoms and is the standard therapy for symptomatic patients and infants diagnosed based on cutaneous and imaging findings. Surgical detethering is likely to be accompanied by debulking and/or resection of any involved tissue, such as the lipoma in this case, as well as repair of any associated neural tube defect or other malformation, such as meningocele. Surgical detethering increases blood flow to the caudal spinal cord and can lead to improved clinical symptoms including improved urodynamics in patients with urinary dysfunction and reduction of pain.

• TCS is a neurologic disorder caused by retraction of the conus medullaris that may be congenital or acquired.
• TCS is most commonly associated with spinal dysraphism and attachment of the filum terminale to the dura mater or skin.
• TCS may be associated with a thickened filum terminale, spinal cord lipoma, spinal dysraphism, anorectal malformations, or spinal cord neoplasms, among other entities.
• Conservative watch-and-wait monitoring may be appropriate for asymptomatic adult patients, while surgical detethering can alleviate symptoms and is the standard therapy for symptomatic patients.

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