Saccular type of limited dorsal myeloschisis

A 3-day-old female presented with complaints of swelling over back in lumbar region since birth, born of non-consanguineous marriage with no other significant birth history.

Examination findings: There was a large cystic swelling in lumbosacral region suspicious for meningomyelocele (Fig 1). Limb movements were normal with no neurological deficit.

MRI spine with brain screening was performed. Multiple vertebral anomalies were seen- i.e. congenital fusion of the L4 and L5 vertebral bodies with L5 butterfly vertebra and spina bifida at L4 level. A large cystic sac-like structure suggestive of meningocele was seen protruding posteriorly through the defect at L4 level containing glial tissue. The lower spinal cord was seen tethered posteriorly due to a linear T2 hypointense structure, attaching the dorsal surface of the cord with the surface of the meningocele, likely a fibro-neural stalk. These findings were suggestive of limited dorsal myeloschisis. The spinal cord was low lying ending at L4-5 level with thickened filum terminale and fibrolipoma. Screening brain revealed small posterior fossa with cerebellar tonsillar ectopia by 6mm. Supratentorial Brain was normal with no hydrocephalus, suggestive of Arnold-Chiari 1 malformation. (Fig 2, 3 and 4)

Background

Limited dorsal myeloschisis (LDM) is a rare form of neural tube defects, without an overtly unfused and exposed neural plate [1]. A focal, closed, midline defect with a fibroneural stalk lying between the skin lesion and spinal cord are the most constant feature of LDM.

Clinical Perspective

In patients with LDM, the most common reason prompting a patient’s referral are skin findings. The most common skin lesion is a skin-covered dimple that appeared as a sunken crater covered with pearly pale epithelium appearing as cigarette burn mark[4]. Children with LDM can have neurologic deficits like lower extremity weakness with urinary dysfunction.

Imaging Perspective:

MRI is the gold standard and the imaging hallmark of LDM is visualization of the stalk that links the skin/posterior subcutaneous lesion to the underlying spinal cord. This stalk may be connected with the vertebral body or dorsally situated without connection to vertebral body. LDM is more frequently seen along the lumbar region and maybe associated with lipomas as compared to dorsal dermal sinus(DDS) which has poorly visible intrathecal tract ending at varying structures and is associated with dermoid/epidermoid tumours. Secondary infections are seen with DDS and not with LDM.

It has been classified as:

1. Saccular LDM: Characterized by CSF signal intensity-membranous sac with a hypointense tract, separate from the filum terminal, that is completely traceable in its entire course. Usually, the attachment site of the tract is the spinal cord just above the conus medullaris. A low-lying conus medullaris and dorsal tenting of the spinal cord at the tract-cord union are seen.
2. Non-saccular LDM: There is a tract with low signal intensity attached to the dorsal aspect of spinal cord with dorsal tenting of the cord by the tract. No membranous sac is seen in subcutaneous tissue.

Outcome

The principal component of the surgical treatment is resection of stalk, regardless of whether the stalk contains neural nodules or complex peripheral nerves [6]. Ligation and cosmetic restoration of the large meningocele sac of the saccular LDM in the cervical or lumbar regions erroneously may cause neurological deterioration in future.

Take-home message/ Teaching points:

The diagnosis of LDM is often missed, which can result in child suffering from neurologic deficits because of the persistence of the tethering element. Possible reasons for a missed diagnosis of LDM are lack of awareness and difficulty of preoperative diagnosis of slender LDM stalk, which can often be confused with a simple meningocele and congenital dermal sinus [2,5].