Tethered cord syndrome (TCS) is abnormal fixation of the conus medullaris in a caudally displaced position. In normal adults, the conus terminates at the L1-2 level; in TCS, the conus may extend below L2-3, even descending to S1-S2. Associated congenital anomalies are frequently found, including thickened filum terminale (>2 mm), fatty infiltration (fatty filum — T1 hyperintense), lipomyelomeningocele, diastematomyelia, dermal sinus tract, or spinal lipoma. Embryologically, it results from secondary neurulation disorder — the filum terminale that should normally regress becomes thickened and/or develops fat infiltration → conus cannot ascend normally. In children, it presents with back pain, lower extremity weakness, sensory loss, foot deformity (pes cavus, equinus), neurogenic bladder, and urinary incontinence. Conus position measurement on sagittal MRI and filum terminale thickness measurement on axial MRI are fundamental diagnostic parameters. Early surgical intervention (filum terminale sectioning) aims to arrest progression of neurological deterioration.
Age Range
0-30
Peak Age
8
Gender
Equal
Prevalence
Uncommon
The pathophysiology of tethered cord syndrome is based on embryological developmental disorder. In normal embryological development, primary neurulation (weeks 3-4) forms the neural tube and secondary neurulation (weeks 5-6) shapes the conus medullaris and filum terminale from the caudal eminence. The terminal ventricle formed during secondary neurulation normally regresses and the filum terminale becomes a thin, fibrovascular structure (<2 mm diameter). In TCS, this regression process is disrupted: the filum terminale abnormally thickens (>2 mm) and/or mesenchymal cells differentiate into adipose tissue → fatty filum (T1 hyperintense signal — reflecting fat content, suppresses on fat-sat sequence). The thickened/fatty filum prevents normal cranial migration of the conus medullaris (from L2-3 at birth to L1-2 by 3 months) → conus remains in caudal position. During growth, the vertebral column elongates faster than the filum terminale → traction on filum increases → mechanical stress and chronic ischemia develop at the caudal end of the spinal cord. This ischemia occurs as traction → compression of vascular bed → decreased perfusion → neuronal metabolic insufficiency. Neurogenic bladder, lower extremity weakness, and sensory loss are clinical reflections of this chronic ischemia. When the filum terminale is surgically sectioned, traction is eliminated → ischemia resolves → neurological progression stops.
Conus medullaris terminating below L2-3 on sagittal MRI with filum terminale showing hyperintense signal on T1 and suppression on fat-sat — the signature finding of tethered cord syndrome. This combination: (1) conus in abnormal caudal position, (2) filum contains fat (embryological regression disorder), (3) fat confirmed by fat-sat → establishes TCS diagnosis with high confidence. Fatty filum is found in approximately 50% of all TCS cases; remaining cases show fibrous thickening (T1 isointense, thickness >2 mm).
Conus medullaris is seen positioned below L2-3 on sagittal T1-weighted images. In cases with fatty infiltration, the thickened filum terminale (>2 mm) shows hyperintense signal on T1 — this fat signal is pathognomonic. The fatty filum is typically seen as a thin hyperintense band extending from the conus tip to the sacrum. Filum diameter is measured on axial T1 images and its position within the thecal sac is evaluated. Posterior positioning of the filum (near the neural foramen) supports tethering.
Report Sentence
Conus medullaris terminates at ___ level on sagittal MRI (normal: L1-2), demonstrating low conus position. Filum terminale is thickened (__ mm) showing hyperintense signal on T1 with suppression on fat-sat; consistent with fatty filum terminale.
Conus medullaris position is clearly evaluated on sagittal T2-weighted images — conus tip is easily identified thanks to high CSF/cord contrast. Conus tip below L2-3 is the diagnostic threshold. On T2, the filum terminale is seen as a thin hypointense band; fatty filum may be isointense or mildly hyperintense on T2. Associated anomalies are also evaluated on T2: syringomyelia (T2 hyperintense cavity within cord), diastematomyelia (cord splitting), lipoma (mildly T2 hyperintense mass).
Report Sentence
Conus medullaris terminates at ___ level on T2-weighted sagittal images demonstrating low conus position; cord signal intensity is normal, no associated syringomyelia is observed.
Fat-sat (fat suppression) sequence plays a critical role in confirming fatty filum terminale diagnosis. Signal loss of the T1 hyperintense filum terminale on fat-sat sequence proves fat content. This finding differentiates from T1 hyperintensity caused by methemoglobin (in hematoma) or proteinaceous content (in mucoid degeneration) — these substances do not suppress on fat-sat. STIR or chemical shift technique can also be used for fat confirmation. Filum position within the thecal sac and diameter are clearly evaluated on axial fat-sat T1.
Report Sentence
Filum terminale shows signal loss on fat-sat sequence confirming that T1 hyperintensity is due to fat content; supporting the diagnosis of fatty filum terminale.
CT plays a complementary role in evaluating bony anomalies in tethered cord syndrome. Spina bifida occulta (incomplete fusion of posterior elements) is the most commonly associated bony anomaly — usually at L5 and/or S1 level. When diastematomyelia is present, bony or cartilaginous septum is superiorly evaluated by CT — while MRI shows soft tissue septum, CT confirms bony septum. Vertebral segmentation anomalies (block vertebra, butterfly vertebra), sacral agenesis, and sacrococcygeal anomalies are also evaluated with CT.
Report Sentence
Incomplete fusion of posterior elements (spina bifida occulta) at ___ level on CT, demonstrating bony anomaly consistent with tethered cord syndrome.
Neonatal spinal ultrasound (posterior acoustic window — through incompletely ossified posterior elements) is an effective screening modality for evaluating conus position and filum terminale thickness. Vertebral level of the conus medullaris is evaluated on sagittal US. Filum terminale thickness is measured on axial/sagittal images; >2 mm thickness is pathological. Fatty filum appears as an echogenic band. Decreased cord mobility (absence of physiological cord pulsation) favors tethering. US loses diagnostic value after 3-6 months when posterior elements ossify → MRI required.
Report Sentence
Conus medullaris terminates at ___ level on spinal US demonstrating low conus position; filum terminale thickness measures __ mm with pathological thickening present.
Criteria
Congenital anomaly present from birth. Associated anomalies frequent: fatty/thickened filum terminale, lipomyelomeningocele, diastematomyelia, dermal sinus tract.
Distinct Features
Symptoms develop in childhood (worsening during growth spurts). Cutaneous stigmata (lumbar hypertrichosis, dermal sinus, subcutaneous lipoma) raise suspicion. Neonatal spinal US screening possible.
Criteria
Re-tethering developing after spinal surgery (myelomeningocele repair, tumor resection, cord untethering). Scar tissue fixes the spinal cord.
Distinct Features
Surgical history is critical. MRI shows scar tissue at surgical site and cord adherence to posterior dura. Contrast MRI helps differentiate scar (enhancing) from tumor recurrence. Re-tethering rate is 20-50%.
Criteria
Conus in normal position (L1-2) but clinical symptoms consistent with TCS. Filum terminale thickened (>2 mm) or pathologically taut. Functional tethering despite normal conus position.
Distinct Features
Most challenging subtype to diagnose. Conus normal on MRI but filum may be thick/fatty. Surgical decision based on clinical findings. Clinical improvement after filum sectioning retrospectively confirms diagnosis.
Distinguishing Feature
Spinal arachnoid cyst is an extramedullary cystic lesion at CSF density (T1 hypo, T2 hyper, FLAIR suppresses); tethered cord has no cystic structure — characterized by low conus + thick/fatty filum terminale. Arachnoid cyst may compress cord but does not affect conus position.
Distinguishing Feature
Tarlov cyst is a perineural cyst at sacral nerve root level with nerve root identified within cyst wall; in tethered cord, conus position and filum terminale pathology are in the foreground. Both pathologies may coexist — Tarlov cysts may be incidentally detected in TCS patients.
Distinguishing Feature
Epidural hematoma is an acquired epidural collection with acute presentation (time-dependent T1/T2 signal); tethered cord is a congenital anomaly with chronic/progressive course. T1 hyperintensity in hematoma is from methemoglobin (no fat-sat suppression); fatty filum T1 hyperintensity suppresses on fat-sat.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralTethered cord syndrome requires early diagnosis and surgical treatment. Surgical indications: symptomatic TCS (bladder dysfunction, lower extremity weakness, progressive scoliosis, foot deformity), definitive pathological MRI findings even without symptoms (markedly low conus, thick fatty filum + associated anomalies). Surgery (filum terminale sectioning) is performed through a small laminectomy — minimally invasive with low complication rate (1-3%). Postoperative prognosis: 70-90% improvement in pain and motor findings in symptomatic patients; bladder function improvement is more variable (40-70%). Delayed diagnosis increases risk of permanent neurological deficit. When asymptomatic low conus is detected (incidental), clinical examination + urodynamic evaluation + 6-12 month MRI follow-up recommended. Neonates with cutaneous stigmata (lumbar hypertrichosis, dimple, subcutaneous lipoma) should be screened with spinal US.
Tethered cord syndrome requires early diagnosis and surgical treatment. Surgery (filum terminale sectioning) aims to stop progression of neurological deterioration. Prognosis after surgery is generally good in symptomatic patients; delayed diagnosis increases risk of permanent neurological deficit. Clinical follow-up is recommended when asymptomatic low conus is detected.