Histological Characteristics of the Filum Terminale in Occult Tethered Cord Syndrome and Filum Terminale Lipoma

Tethered spinal cord syndrome is a neurological disorder characterized by pathological tethering of the spinal cord, leading to neurological, urological, and orthopedic dysfunction. Occult tethered cord syndrome (OTCS) presents with similar clinical manifestations but lacks definitive radiological evidence, whereas filum terminale lipoma (FTL) involves adipose infiltration of the filum terminale, contributing to spinal traction. The histopathological characteristics of the filum terminale in these conditions remain incompletely understood.

To characterize the histological features of the filum terminale in OTCS and FTL.

Filum terminale specimens were obtained from 17 patients with OTCS and 22 patients with FTL undergoing surgical untethering (April 2020-April 2024) and from six cadavers as reference samples. The histopathological evaluation included hematoxylin-eosin, Masson trichrome, and Elastica van Gieson staining. Immunohistochemistry assessed collagen types I and III.

OTCS cases showed reduced collagen type I, sparse and irregularly looped elastic fibers, capillary dilation, and hyaline-like degeneration. FTL specimens exhibited adipose infiltration, densely packed and elongated elastic fibers, and intense collagen type I staining, although some showed reduced elasticity. Cadaveric samples displayed normal histology without degeneration.

The observed decrease in collagen type I and elastic fibers in OTCS suggests compromised filum terminale elasticity, potentially contributing to pathological tethering. In FTL, adipose infiltration is the primary factor driving spinal cord traction, although some cases also showed reduced elastic fiber integrity. These findings emphasize the importance of further research into the relationship between histopathological changes and clinical presentations. Better understanding of this correlation is crucial for developing standardized management strategies.