Tight filum terminale syndrome

Tight filum terminale syndrome, or tight filum syndrome, is a subtype of the tethered cord syndrome that is attributed to a thickenedthick, short, and/or inelastic filum terminale rather than other tethering agents.

Terminology

The term "tight filum terminale syndrome" is relatively uncommonly used in the literature comparedsynonymous to the umbrella term "tethered cord syndrome" secondary to a "tight filum terminale." More commonlyThe emphasis on "syndrome" highlights a clinical diagnosis made by the synthesis of symptoms, neurologic exam signs, and laboratory tests such as urodynamics. In contrast, "tight filum terminale" is a pathoanatomic finding, which may or may not be visible radiologically and associated with the clinical syndrome.

When the clinical syndrome may be attributedis present but imaging is normal (conus medullaris is normally positioned, filum terminale appears normal in size and signal, and other tethering agents are absent), the term occult filum terminale syndrome is used to the anatomic/imaging findings of "tightimply that an inelastic but grossly normal-appearing filum" ³.

The thickening terminale may be due to fibrous tissuethe culprit ^2,4. This diagnosis remains controversial ⁷. The term occult tethered cord syndrome is synonymous as a histologic abnormality in the filum terminale is the implied diagnosis by exclusion ⁸.

Epidemiology

In one surgical case series of children treated for tethered cord syndrome, with or without associated filar cysts or filar lipomatight filum terminale was the cause in 16% ¹³.

Pathology

The condition is caused by incomplete involution of the distal spinal cord during development ¹. 

Radiographic features

The diameter of theTwo major anatomic findings characterize tight filum terminale exceedssyndrome ⁵:

• short filum: low-lying conus medullaris terminating inferior to L2
• thick filum: greater than 2 mm atdiameter, often fatty

Either, both, or neither finding can be seen in the level of L5-S1syndrome; i.e., an inelastic tight filum could have strictly normal imaging findings ⁶. Additional findings are noted below.

Ultrasound

There ismay be reduced motion of the conus medullaris ¹, which extends below.

MRI

A fatty filum shows high signal on T1-weighted images.

A tight filum is usually dorsally positioned (in contact with the levelposterior dura rather than in between the cauda equina nerve roots), especially on prone imaging ^6,8. There may be gradual tapering of the inferior endplateconus medullaris into the filum and the distal spinal cord appears straight (tense) rather than curved (relaxed), although these findings have unclear reliability ⁶.

Treatment and prognosis

The treatment is surgical sectioning of the L2 vertebral bodylower end of the filum. The vast majority (90%) of children with tight filum terminale have stable to improved neurologic function following surgery ³.