Myelomeningocele and myelocele are both midline bone defects through which meninges and/or neural placode (unfolded spinal cord) are visible; most discovered by in utero sonography or magnetic resonance imaging (MRI).

In a myelomeningocele (the most common type, 0.1% of live births), the neural placode and meninges protrude above the skin; it almost always is seen in the context of a Chiari 2 malformation and is generally sporadic but may affect subsequent siblings.

In a myelocele (less common), the neural placode is flush with the skin.

Both entities are untethered and closed at birth, and imaging is done for recurrent symptoms. Prenatal surgery is effective in closing it and minimizing intracranial findings of Chiari 2 and hydrocephalus.

For practical purposes, after repair of one of these defects, all spinal cords are retethered (due to scar), and imaging studies are mainly used to exclude other abnormalities, such as syringomyelia (30% to 75%), diastematomyelia (30%), lipomas, dermoids, and epidermoids.

Both lipomyelomeningocele and lipomyelocele refer to a midline bone spinal defect covered by skin that may have a dermal sinus, hairy patch, or hemangioma above the intergluteal fold.

In a lipomyelocele, meninges and neural placode are located at the level of a spina bifida but covered by a lipoma and skin.

In a lipomyelomeningocele, the meninges and neural placode protrude through a bone opening but are covered by a lipoma and skin; this lipoma is in direct contact with the surface of the neural placode, and the patients have a prominent mass in the low back.

Both lesions may be detected at birth or be mostly clinically silent and not found until adulthood.

A filar lipoma is the most common intraspinal lipoma; it occurs in 1% to 6% of the population and is generally an incidental and asymptomatic finding.

With a filar lipoma, the filum terminale is thickened (generally, its normal size should not exceed that of neighboring nerve roots) and has fat within it.

In the presence of a filar lipoma, if the conus medullaris is normal in position, then the findings are probably not clinically significant; however, if the conus medullaris is abnormally low, consider the diagnosis of the tight filum terminale syndrome.

Intradural lipomas are rare and are mostly found in the cervical region but may occur anywhere in the spine; most become symptomatic by 5 years of age and result in paresis, spasticity, sensory loss, weakness, and bowel/bladder dysfunction.

Main differential diagnosis: dermoid/epidermoid, teratoma.