Lipomyelomeningocele

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Status

Done

Definition

A subcutaneous lipoma that passes through a midline defect in the lumbodorsal fascia, vertebral neural arch, and dura, and merges with an abnormally low tethered cord.

Aka

Lipoma of the cauda equina

Type 2 spinal lipomas

Classification

Terminal

Dorsal

Transitional (between the two)

Numbers

These lipomas account for 20% of covered lumbosacral masses.

Pathology

In addition to being abnormally low, the conus medullaris is split in the midline dorsally usually at the same level as the bifid spine, and this dorsal myeloschisis may extend superiorly under intact spinal arches.

There is a thick fibrovascular band that joins the lamina of the most cephalic vertebrae with the bifid lamina.

This band constricts the meningocele sac and neural tissue, causing a kink in the superior surface of the meningocele.

Asymptomatic lipomas of the filum terminale occur in 0.2–4% of MRIs.

The dura is dehiscent at the level of the dorsal myeloschisis, and reflects onto the placode.

The lipoma passes through this dehiscence to become attached to the dorsal surface of the placode, and may continue cephalad under intact arches with the possibility of extension into the central canal superiorly to levels without dorsal myeloschisis.

The lipoma is distinct from the normal epidural fat which is looser and more areolar.

The subarachnoid space typically bulges to the side contralateral to the lipoma.

Clinical presentation

Symptoms are due to

Tethering of the spinal cord, especially during growth spurts,
Compression due to progressive deposition of fat, especially during periods of rapid weight gain

Paeds

56% presented with a back mass
32% with bladder problems
10% because of foot deformities, paralysis or leg pain

Physical examination

Almost all patients have cutaneous stigmata of the associated spina bifida:

fatty subcutaneous pads (located over the midline and usually extends asymmetrically to one side) with or without dimples, port-wine stains, abnormal hair, dermal sinus opening, or skin appendages.
Clubbing of the feet (talipes equinovarus) may occur.
The neurologic exam may be normal in up to 50% of patients (most presenting with skin lesion only). The most common neurologic abnormality was sensory loss in the sacral dermatomes.

Evaluation

Plain LS spine X-rays will show spina bifida in most cases.

Present in almost all by definition, but some may have segmentation anomalies instead, such as butterfly vertebra (p.232).

Abnormalities of fusion and sacral defects may also be seen. The abnormally low conus can be demonstrated on myelogram/CT or on MRI. MRI also demonstrates the lipomatous mass (high signal on T1WI, low signal on T2WI). All patients should have pre-op urological evaluation to document any deficit

Surgery

Goals

Release the tethering
Reduce the bulk of fatty tumor

Do not perform simple cosmetic treatment of the subcutaneous fat pad

As it does not prevent neurologic deficit, and may make later definitive repair more difficult or impossible

Indication

Patient reaches 2 months of age, or at the time of diagnosis if the patient presents later in life

Adjuncts

Evoked potential monitoring
Laser

Surgical technique (modified)

Mobilize the subcutaneous mass, it funnels down through the deep fascia

Open last intact vertebral arch (work from normal dura)

Identify the fibrovascular band that crosses the most cephalic widely bifid lamina

Sectioning the fibrovascular band frees the dural tube and releases the sharp kink in the superior surface of the meningocele

Taking care to preserve dorsal nerve roots, the dura is incised anterior to the dura-lipoma junction

Similar procedure is carried out with arachnoid membrane

Dural/arachnoid incisions are continued around entire extent of tethered conus

Cord and placode are untethered; monitoring techniques described in Tethered cord syndrome (p.287) are an option

Subtotal removal of lipoma: lipoma is then trimmed as completely as possible, intentionally leaving some fat behind to avoid injury to dorsal surface of placode. Superior extension along dorsal surface of cord or into central canal is debulked as much as is safely possible

The placode is reformed into a closed neural tube

Close the pial margins

The dura is closed (primarily if possible, or using fascia lata graft if too much tension is placed on folded placode)

Outcome

Surgery

19% will improve
75% will be unchanged
6% will worsen
Foot deformities often progress regardless.

DDx

Feature	Lipomyelomeningocele	Lipomyelocele
Definition	Closed neural tube defect with herniation of neural tissue, CSF, and meninges through a dysraphic spine, plus a spinal lipoma contiguous with subcutaneous tissue and attached to dorsal neural placode	Closed spinal dysraphism with lipoma attached to neural placode, neural placode and lipoma remain within the spinal canal without meningeal herniation
Placode-Lipoma Junction	Lies outside the spinal canal with dorsal extension of meninges through bony defect (meningocele present)	Lies inside the spinal canal; no meningeal herniation beyond spinal canal
Skin coverage	Intact skin over the lesion	Intact skin over the lesion
Radiologic findings	Expanded spinal canal, herniation of neural placode, meninges, lipoma; low-lying tethered cord; often with vertebral anomalies	Lipoma and placode identifiable within spinal canal; dilated spinal canal but no herniation of meninges outside canal
Clinical presentation	Soft tissue mass in lower back, cutaneous stigmata (e.g., hair tuft, dimple), neurological symptoms due to tethering	Similar skin findings but no meningocele; neurological symptoms due to tethered cord possible
Surgical considerations	Complex due to meningocele and neural involvement outside canal	Less extensive than lipomyelomeningocele, as no meningeal sac herniation
Common location	Lumbar and lumbosacral region	Lumbar and lumbosacral region
Embryological basis	Defect in primary neurulation with meningeal protrusion	Defect in neural tube closure without meningeal sac protrusion

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