Tight filum terminale syndrome is caused by incomplete involution of the distal spinal cord during embryogenesis. This leads to development of an abnormally thickened filum terminale, which may be associated with lipomas or cysts within the filum.
Clinical symptoms are due to stretching of the spinal cord with resulting vascular insufficiency at the level of the conus medullaris. These symptoms can occur at any age, may be unspecific, and consist of neurologic deficiencies, pain or dysesthesia, and bladder or bowel dysfunction.
Spinal US shows an abnormally thickened filum terminale, sometimes in combination with a centrally located small cyst or lipoma.
By definition, the diameter of the filum terminale exceeds 2 mm (normal range, 0.5–2 mm) at the level of L5-S1. Owing to the presence of tethering, the tip of the conus medullaris is located below L2-3.