13/02/2026
What is the difference between Tethered Cord (TC) and Occult Tethered Cord?
Tethered Cord Syndrome (TCS) is defined as a stretch-induced functional disorder of the spinal cord wherein the caudal spinal cord is mechanically anchored by an inelastic structure. The classical diagnostic criteria mandate the convergence of clinical symptomatology with macro-anatomical radiographic anomalies. Specifically, the conus medullaris is visualized terminating below the L2 vertebral level, often accompanied by a thickened filum terminale (>2 mm) or spinal dysraphisms (e.g., lipomyelomeningocele) [Hertzler et al., 2010; Yamada et al., 2004].
In contrast, Occult Tethered Cord Syndrome (OTCS)—also referred to as Tight Filum Terminale Syndrome with a normal conus—presents a diagnostic challenge. It describes a subset of patients who exhibit the classic metabolic and ischemic symptomatology of TCS but present with a structurally normal conus position (at or above the L1-L2 disc space) and often a filum of normal thickness on standard supine MRI [Steinbok et al., 2007; Warder & Oakes, 1993]. In these cases, the pathology is attributed to decreased viscoelasticity of the filum rather than gross anatomical malposition.
2. Radiographic Assessment: Supine vs. Prone MRI
Standard Supine Lumbosacral Magnetic Resonance Imaging (MRI) remains the gold standard for identifying classic TCS. It effectively visualizes the low-lying conus and associated masses. However, its sensitivity is significantly reduced in OTCS, where the static supine position may mask the mechanical tension of the filum.
To address this, the Prone MRI protocol has emerged as a critical adjunctive diagnostic tool.
• Physiological Rationale: In a prone (face-down) position, gravity should naturally displace a non-tethered spinal cord and filum terminale anteriorly (ventrally) within the thecal sac.
• Pathological Findings: In OTCS, the loss of filum compliance prevents this anterior migration. A lack of anterior displacement, or the visualization of the filum remaining not completely anterior in the thecal sac during prone imaging, serves as a surrogate marker for mechanical tethering.
• Nerve Root Trajectory: Prone imaging may also reveal dorsal angulation of the nerve roots, suggesting posterior traction even in the absence of conus descent.
3. Functional Diagnostics and Symptomatology
Given the ambiguity of static imaging in OTCS, functional verification is mandatory.
• Urodynamics (UDS): Neurogenic bladder dysfunction is a hallmark of occult tethering. Studies indicate that urodynamic abnormalities (e.g., detrusor overactivity, dyssynergia) are present in up to 73% of patients with OTCS and may improve following filum sectioning [Metcalfe et al., 2006].
• Neurophysiology: Somatosensory Evoked Potentials (SSEP) and Motor Evoked Potentials (MEP) provide objective data on dorsal column and corticospinal tract integrity, respectively. While useful, normal SSEP/MEP findings do not rule out OTCS due to the intermittent nature of the ischemic insults [Sala et al., 2007].
Clinical Presentation Profile:
The symptomatology is consistent across both Classic TCS and OTCS, characterized by the triad of:
1. Urological/Gastrointestinal: Urinary frequency, incontinence, retention, recurrent UTIs, and constipation/encopresis.
2. Neurological: Lower extremity paresis, paresthesias, and gait disturbances.
3. Musculoskeletal: Lumbosacral pain (often exacerbated by flexion) and non-dermatomal leg pain.
