What is the gross morphology of Spina Bifida (congenital defect of the spine)?

From the Guidelines

Spina bifida is a neural tube defect characterized by incomplete closure of the vertebral arches and spinal cord malformation, with three main forms: spina bifida occulta, meningocele, and myelomeningocele, each with distinct gross morphology. The gross morphology of spina bifida varies depending on the type, with spina bifida occulta being the mildest form, characterized by a small defect in the vertebral arch without visible external abnormalities, often marked only by a dimple, tuft of hair, or skin discoloration over the affected area 1. Meningocele presents as a sac-like protrusion containing cerebrospinal fluid and meninges that extends through the vertebral defect but does not contain neural tissue. Myelomeningocele, the most severe form, features a sac containing both meninges and neural elements (spinal cord and/or nerve roots) protruding through the defect, with the neural tissue exposed or covered only by a thin membrane 1.

Key Characteristics of Spina Bifida

• The defect typically occurs in the lumbosacral region but can affect any level of the spine
• Associated findings may include Chiari II malformation (hindbrain herniation), hydrocephalus, and various neurological deficits corresponding to the level and severity of the lesion
• The underlying embryological cause is failure of the neural tube to close completely during the fourth week of gestation, resulting in these characteristic anatomical abnormalities

Clinical Implications

The economic impact of spina bifida is significant, with estimated total lifetime medical expenses adjusted for inflation increasing from $236,000 to $319,000 in just 20 years 1. Urological issues can be a significant source of morbidity and mortality, and are implicated as a cause of death in almost a third of patients with open spina bifida followed long term. Therefore, early diagnosis and management of spina bifida are crucial to prevent long-term complications and improve quality of life.

From the Research

Gross Morphology of Spinal Bifida

The gross morphology of spinal bifida is characterized by a congenital disorder with incomplete closure of the spinal column due to a bony vertebral defect 2. The term spina bifida literally means cleft spine and is used as a generic term of spinal dysraphism.

• The insufficient closure of one or more vertebral arches is the result of an incomplete junction of the neural tube 2.
• Depending on the extent of the neural tube defect, various types of spina bifida can be differentiated, including:
  • Closed spinal dysraphisms, also known as spina bifida occulta, which are solely characterized by a bony defect of the vertebral arch 2.
  • Spina bifida cystica (synonym: open spina bifida or spina bifida aperta), which can be distinguished by a protruding cyst, containing either meninges or meninges in combination with spinal cord tissue and are defined as open spinal dysraphisms 2.
• The most frequent spina bifida phenotype is myeloschisis, which is characterized by an open neural plate with exposed ependyma 3.
• Other subtypes of spina bifida include myelomeningocele, meningocele, and unspecified spina bifida aperta (SBA) subtype 3.

Subtypes of Spina Bifida

The subtypes of spina bifida can be classified into:

• Spina bifida occulta (SBO) 3
• Spina bifida aperta (SBA), which includes:
  • Meningocele 3
  • Myelomeningocele 3
  • Myeloschisis 3
  • Unspecified SBA subtype 3

Neuropathological Findings

Neuropathological findings in spina bifida cases often include:

• Hydrocephalus 4
• Chiari II malformation 4
• Heterotopia 4
• Cerebellar anomalies 4
• Gyrification defects 4
• Ependymal denudation 4