Thoracic limited dorsal myeloschisis with diastematomyelia in neonate

A neonate presented at birth with a large swelling in the midline at the lower thoracic spinal level. The baby had no other clinical/neurological abnormality and no cutaneous birthmarks. The baby was referred for Ultrasonography (USG), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI) of the spine for further evaluation.

USG of the spine revealed a well-defined cystic lesion at the level of the lower thoracic spine with a few linear hyperechoic structures within. Vertical splitting of the spinal cord into two was noted. CT of the thoracic spine showed splaying of the posterior vertebral elements of T3 to T8 vertebrae with a bony spur in the spinal canal at the midline at the level of the T8 vertebra and a large well-defined hypodense lesion of fluid density with suspicious communication with the spinal canal.

MRI of the spine showed a large well-defined T1 hypointense, T2 and STIR hyperintense lesion with T2 and STIR hypointense stalk-like structure, extending from the spinal cord at the level of the T6–T7 vertebrae. Sagittal splitting of the spinal cord was noted from the level of T4 to T8 vertebrae. No abnormal signal intensity in the spinal cord. Conus medullaris ends at L1–L2 level. The craniocervical junction was normal. Screening T2 MRI of the brain was normal.

Background

Spinal dysraphisms (SDs) are congenital malformations of the spine. They are a subtype of neural tube defects, which are the second most common birth anomalies. The prevalence ranges from 1 to 3 per 1000 live births. Genetic and non-genetic factors such as folic acid deficiency, maternal obesity, and tobacco exposure play a role in the development of SDs. They occur due to impaired gastrulation or neurulation. The lumbosacral spine, followed by the thoracic spine, is the most common sites [1]. Spina bifida is the misclosure of vertebral arches [2]. Open SDs are characterised by a defect in the overlying skin, and closed SDs are covered by skin [3]. Limited dorsal myeloschisis (LDM) is a rare type of neural tube defect, which occurs due to incomplete separation of cutaneous and neural ectoderms, retained as a persistent neuroectodermal link without an unfused or exposed neural plate [4]. Diastematomyelia is the sagittal splitting of the spinal cord that occurs due to abnormal adhesion between ectoderm and endoderm, which may be fibrous, cartilaginous, bony, or a combination [5].

Clinical Perspective

SDs can cause neurological impairment and may be associated with other malformations [1]. Open SDs and closed SDs with a subcutaneous mass can be detected by clinical examination at birth [3]. Closed SDs without subcutaneous mass may be occult or may have skin markers such as skin tags, sacral dimples, and hairy patchy [6].

Imaging Perspective

USG can be used in the neonatal period for the evaluation. CT has a limited role due to its poor tissue contrast. MRI is optimal for evaluation using a target protocol consisting of high-resolution T1 and T2 sequences in multiple planes [1].

LDM is characterised by a skin-based, CSF-filled sac and fibroneural stalk connecting the sac with the spinal cord. It can be saccular or non-saccular type [4,7]. Cervicothoracic cystic dysraphisms have 3 subtypes: 1 – cystic mass with stalk-like structure (stalk extends from the dorsal surface of the spinal cord to the posterior wall of cystic mass); 2 – cystic mass containing hydromelic spinal cord (myelocystocele); 3 – cystic mass containing only CSF (meningocele) [8]. It has a better prognosis than myelomeningocele [4,7].

Myelomeningocele is characterised by the expansion of the subarachnoid space protruding through an open spina bifida, with nerve roots coursing through the expanded subarachnoid space. In contrast to myelomeningocele, no expansion of the subarachnoid space is seen in myelocele and myeloschisis. Hemimyelomeningocele is characterised by the exposure of the hemicord to the environment with the expansion of the subarachnoid space. Lipomyelomeningocele is characterised by subcutaneous lipoma, and myelomeningocele with cord-lipoma interface outside with vertebral arches. Meningocele has no neural elements within and is covered by skin. Myelocystocele is the herniation of the hydrosyringomyelic cavity through spina bifida into a meningocele. Diastematomyelia is characterised by two hemicords. In type 1 diastematomyelia, both hemicords have individual dural sacs separated by a septum. In type 2 diastematomyelia, a single dural sac contains both hemicords [1].

Outcome

Neuroimaging is helpful in the diagnosis of SDs, associated abnormalities, vertebral numbering, and presurgical evaluation [1]. Classification of the type of diastematomyelia and associated abnormalities is needed to decide the surgical management [6,9]. It can lead to significant morbidity and poor prognosis if diagnosed late or untreated [10].

Teaching Points

MRI is valuable for the diagnosis of SDs and is helpful in deciding prompt surgical management.

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