Introduction to Occult Spinal Dysraphism
Occult spinal dysraphism (OSD) is known as a group of congenital and pathological changes occurring in the spine and spinal cord that are united by similar embryological causes, common forms of presentation, and a propensity for multiple expressions within a single patient. These entities encompass the split cord anomalies, tethered cord induced by a tight ter-minal filum, neurenteric cyst, meningocele manqué, terminal syrinx, lipomyelomeningocele, and dermal sinus tract with intradural dermoids.

The development of OSD is also linked to open neural tube defects because additional pathological expression is often found within the myelomeningocele. Near the area of the placode the cord may split, the filum may be too robust, or a number of other changes may occur. In families in which one child has some form of OSD the mother's subsequent neonates appear to have the same risks (3.5%) of developing an open neural tube defect as if the first child had a myelomeningocele.

These lesions are important for all physicians to recognize. Prophylactic surgery has a high likelihood of changing the natural history in which a gradual loss of function may be replaced by clinical stability. Although the disease in many patients will be recognized in infancy and childhood because of cutaneous signs, at least one third of patients may not have apparent skin changes. The onset of signs and symptoms may be so gradual that a patient's initial presentation to a neurosurgeon may not be until adulthood. It is for all of these reasons that it behooves the neurosurgical community to be knowledgable about this complex and fascinating group of problems.