Canine Occult Tethered Cord: Dynamic MRI “fixed conus” + new severity score predict which dogs need surgery

Occult tethered cord syndrome: insights into clinical and MRI features, prognostic factors, and treatment outcomes in 30 dogs with confirmed or presumptive diagnosis

Javier Espinosa Romero; Steven De Decker; Koen Santifort; Rodrigo Gutierrez-Quintana; Maria Ortega; Ane Uriarte; Abtin Mojarradi; Quinten van Koulil; Despoina Douralidou; Irene Espadas; Miguel Benito Benito; Carlo Anselmi; Charlotte Dye; Patricia Alvarez; Juan José Minguez; Abbe Crawford; Christoforos Posporis.

Background

Tethered cord syndrome (TCS) results from abnormal traction on the conus medullaris (CM) and related structures; when routine MRI appears normal but signs fit TCS, the condition is termed occult TCS (OTCS). Veterinary descriptions are sparse, and diagnosis is challenging; dynamic lumbosacral MRI assessing (lack of) physiological CM translocation has been proposed to raise suspicion in the absence of alternative causes. This multicenter study aimed to characterize clinical phenotype, MRI features, outcomes, and prognostic factors in canine OTCS.

Methods

Retrospective, descriptive, multicenter cohort from referral centers in the UK, Spain, the Netherlands, and Sweden (ethical approval URN SR2024–0012). Client-owned dogs with L4–S3/cauda-equina localizing signs and unremarkable neutral-position MRI of thoracolumbar–lumbosacral–tail base were included; dynamic MRI was evaluated when available but not required. Surgically treated cases with positive postoperative response were classified as confirmed OTCS (C-OTCS); medically managed cases were presumptive OTCS (P-OTCS). A novel 16-point clinical severity score (with behavior items) provided neurological grading (I–IV). Dynamic MRI was reviewed for fixed CM/dural sac position (no cranio-caudal translocation).

MRI studies were predominantly high-field (1.5 T); sequences included T2-weighted, STIR, heavily T2-weighted, gradient-echo, 3D FIESTA, and pre/post-contrast T1-weighted. Twenty dogs underwent dynamic MRI, and CM/dural-sac termination levels were recorded using a standardized vertebral/IVD-based scheme.

Results

Thirty dogs met criteria: 11 surgically treated (all responders, classified C-OTCS) and 19 medically managed (P-OTCS). Presentations spanned 2012–2025.
Owner-reported signs were dominated by pain/dysesthesia (29/30, 97%), followed by gait abnormalities (70%), impaired physical activity (63%), and urinary/fecal incontinence (17%); behavioral abnormalities were frequent (67%). Neurological deficits were recorded in most dogs.

On MRI, median CM termination was at L7 and dural-sac termination at S1/cranial sacrum. In 19 interpretable dynamic studies, none showed physiological cranio-caudal translocation—consistent with a fixed CM/DS.
Electrodiagnostic testing (9 dogs) showed abnormalities in 4/9 (44%), all three P-OTCS dogs with abnormalities also had a fixed CM on dynamic MRI.

Outcomes at last follow-up: across the cohort, full recovery in 10/27 with outcome data (37%); by group, C-OTCS 7/11 (64%) full recovery and P-OTCS 3/19 (16%) full recovery; partial recovery was common (43% overall). Short-term after surgery, 9/11 (82%) achieved full recovery, with some later partial relapses; two relapsed dogs improved after revision surgery. Seventeen dogs (57%) were still receiving medical therapy at last follow-up.

Prognostic analyses: Lower clinical-severity scores predicted response to medical therapy (AUC 0.90; optimal threshold score = 7). Worsening evolution before referral, behavioral abnormalities, and higher neurological grade were each associated with poor medical response. Surgical treatment was significantly associated with full recovery and being off medication at last follow-up.

Surgical notes (C-OTCS): lumbosacral dorsal laminectomy with dissection of FTe alone (n=5) or both FTe+FTi (n=6); tight/thickened filum was commonly recorded, and cranial displacement of DS/CM after FT dissection was often observed.

Limitations

Retrospective, multicenter design with non-standardized MRI protocols and reliance on clinical records; dynamic MRI was not uniformly performed; five surgical cases lacked FT histopathology; P-OTCS cases lacked surgical confirmation; small sample size precluded multivariable adjustment. Inter-/intra-observer agreement for imaging was not assessed because reads were by consensus only. Follow-up duration and medical protocols varied.

Conclusions

In dogs with suspected OTCS, a fixed CM (and/or dural sac) on dynamic lumbosacral MRI, coupled with compatible clinical signs and exclusion of alternatives, characterizes the syndrome. Surgical detethering was associated with higher odds of full recovery and discontinuation of medical therapy, though relapse occurred in some cases. A 16-point clinical-severity score and derived neurological grades showed utility in predicting medical treatment response (threshold ≈ 7), warranting external validation.

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