Tethered Cord & Spinal Dysraphism

Epidemiology

Incidence

Collectively common in paediatric neurosurgical practice; precise population incidence varies by subtype and by the radiological threshold used to define a low conus or a thickened filum.

Age peak

Two patterns: cutaneous stigmata recognised in infancy, and growth-related deterioration that classically clusters around periods of rapid linear growth, including adolescence.

Location

Lumbosacral cord, conus medullaris, and filum terminale; the involved level determines the deficit pattern.

Clinical Presentation

• Cutaneous (the bedside red flags, often the earliest sign): midline lumbosacral lipomatous mass, atypical or high dimple, hairy patch (hypertrichosis), capillary malformation, skin tag or tail-like appendage, or a dermal sinus ostium.
• Urological (frequently the earliest functional evidence): a neuropathic bladder with incontinence, retention, or recurrent urinary tract infection; new wetting after established continence is a particular alarm.
• Neurological: asymmetric lower-limb weakness, sensory change, hyporeflexia or hyperreflexia, and gait disturbance.
• Orthopaedic: foot deformity (cavus, asymmetric foot size), leg-length discrepancy, and scoliosis, particularly early or atypical curves.
• Pain: low back or leg pain, sometimes exacerbated by activity or flexion, more often reported by older children and adolescents.

Imaging

• MRI of the whole spine is the diagnostic standard: defines conus level, filum thickness and fat, any lipoma, dermal sinus trajectory, and split cord anatomy, and screens the entire neuraxis for associated anomalies.
• Spinal ultrasound is useful before posterior-element ossification (broadly under about 3 months of age) and for the initial work-up of a cutaneous marker, but does not replace MRI when concern persists.
• The conus normally reaches its adult level (tip at or above the L2 to L3 disc space) by about 2 to 3 months of age; a conus persistently below L3 is abnormal, although a normal-level conus does not exclude a symptomatic tight filum.

Pathology & Molecular

Histology. Substrate-dependent (fibrolipomatous filum, lipoma fused to placode, epithelial sinus tract, septated cord). The shared functional lesion is traction-related lumbosacral cord dysfunction rather than a single histology.

Molecular. Most closed dysraphisms are sporadic and multifactorial; specific monogenic forms are uncommon. The experimental basis of the syndrome is impaired mitochondrial oxidative metabolism in the cord under traction (Yamada et al., 1981), with measurable recovery after untethering.

Management

Surgery. Symptomatic tethered cord is treated by microsurgical untethering directed at the specific anatomy (filum section, lipoma resection and placode reconstruction, dermal sinus excision, or division of a split-cord septum). Intra-operative neuromonitoring is standard. The management of the radiologically tethered but wholly asymptomatic child is genuinely contested and is addressed in the entries that follow.

Adjuvant therapy. Multidisciplinary care is essential, in particular paediatric urology (with urodynamics) and orthopaedics; physiotherapy and bladder management support function around surgery.

Considerations. Establish a functional baseline before intervening: a documented neurological examination and baseline urodynamics make subtle later change interpretable and inform the decision to operate.

Outcomes

Untethering reliably arrests progression in most symptomatic children. Pain and recently acquired bladder dysfunction may improve; established motor deficit, fixed foot deformity, and long-standing bladder denervation usually stabilise rather than reverse. The earlier in the symptomatic course the cord is released, the more function is preserved.

Substrates of the tethered cord (covered in this module)

Epidemiology

Incidence

A common closed dysraphism; exact figures depend on the radiological definition used.

Age peak

Recognised across childhood; symptomatic presentation often coincides with growth.

Location

Filum terminale / conus, almost always lumbosacral.

Clinical Presentation

• Often a cutaneous marker (dimple, small lipoma, hairy patch, capillary malformation) prompts imaging in an otherwise well infant.
• Symptomatic presentation: neuropathic bladder, lower-limb or foot changes, back or leg pain, and atypical or early scoliosis.
• Examination may be normal in early disease, which is why baseline urodynamics is valuable.

Imaging

• MRI: assess conus level, filum diameter (>2 mm at L5 to S1 is the commonly cited threshold), and fat within the filum (T1 hyperintensity); a fibrolipoma of the filum is a frequent finding.
• A normal-calibre, normally positioned filum on MRI does not entirely exclude a symptomatic tight filum; correlation with the clinical and urodynamic picture is essential.
• Image the whole spine to exclude a second, more complex tethering element.

Pathology & Molecular

Histology. Fibrous and/or fibrolipomatous filum, sometimes with reduced elasticity; a fibrolipoma of the filum is common.

Molecular. Sporadic; no consistent monogenic basis.

Management

Surgery. Section of the filum through a limited lumbosacral exposure and small laminotomy. The filum is positively identified (by its position, appearance, vessel on its dorsal surface, and intra-operative stimulation characteristics, distinguishing it from a nerve root) and divided. The procedure is short and generally low-morbidity.

Adjuvant therapy. Urological assessment with urodynamics where bladder symptoms exist.

Considerations. Correct identification of the filum versus a sacral nerve root is the critical safety step; intra-operative neuromonitoring (including stimulation and the bulbocavernosus reflex) supports this. The decision to operate on a normal-conus, minimally symptomatic child should be individualised and explicitly discussed with the family.

Outcomes

Filum section reliably halts progression. Pain and recent-onset bladder symptoms frequently improve; established deficits stabilise. Retethering after simple filum section is uncommon compared with lipoma surgery.

Epidemiology

Incidence

Account for a substantial proportion of closed spinal dysraphism in surgical series.

Age peak

Frequently detected in infancy through a lumbosacral fatty mass or other cutaneous marker; symptomatic deterioration may follow with growth.

Location

Lumbosacral; the lipoma-placode interface and its relation to the dura define the subtype.

Clinical Presentation

• A soft midline or paramedian lumbosacral fatty mass is the typical presenting sign, often with additional cutaneous markers.
• Neuro-urological deterioration (bladder dysfunction, lower-limb weakness, sensory change, foot deformity) may be present at diagnosis or develop subsequently.
• Many infants are neurologically intact at presentation, which is precisely what makes the timing-of-surgery question difficult.

Imaging

• MRI characterises the lipoma subtype (dorsal, transitional, terminal, chaotic), the position of the cord-lipoma interface relative to the dural sac, and the conus level.
• Define the relationship of the placode to the lipoma and to the dura before surgery; this drives the operative plan and the risk assessment.
• Whole-spine imaging to exclude additional anomalies.

Pathology & Molecular

Histology. Mature adipose tissue continuous with a dysplastic neural placode; the cord-lipoma junction is the surgical plane of interest.

Molecular. Sporadic; multifactorial.

Management

Surgery. Microsurgical untethering with resection of the lipoma and reconstruction of the placode. Two philosophies are debated: partial (subtotal) resection with untethering, versus total or near-total resection with radical pia-to-pia reconstruction of the placode to reduce the cord-sac ratio and limit retethering (Pang et al., 2009). Intra-operative neuromonitoring is integral. The asymptomatic infant poses a genuine dilemma: prophylactic surgery aims to prevent later deterioration, but carries operative risk, and not all asymptomatic lipomas become symptomatic; practice varies between centres and is individualised.

Adjuvant therapy. Lifelong multidisciplinary surveillance (urology with periodic urodynamics, orthopaedics).

Considerations. Retethering is the central long-term problem in this group, more so than after simple filum section. The operative aim is a generous, low cord-to-sac ratio and a free conus, achieved with the least neural risk.

Outcomes

Untethering arrests progression in most symptomatic children; reversal of established deficit is limited.

By molecular subgroup: Symptomatic retethering is the principal cause of late deterioration. Series advocating total/near-total resection with radical placode reconstruction report lower symptomatic retethering than historically reported for partial resection (Pang et al., 2009); chaotic and large transitional lipomas remain the most difficult to resect completely and carry the least favourable anatomy.

Conus lipoma subtypes (operative relevance)

Epidemiology

Incidence

An uncommon but clinically important closed dysraphism; the lumbosacral region predominates, with occipital and other midline sites also occurring.

Age peak

The ostium is present from birth; presentation ranges from an incidental skin finding to infection at any age.

Location

Midline, most often lumbosacral; the level of the cutaneous ostium does not reliably predict the depth of the tract.

Clinical Presentation

• A midline dorsal pit or ostium, sometimes with a hair tuft, capillary malformation, or subtle swelling.
• Infective presentation: recurrent meningitis (especially with unusual or skin organisms), or an intraspinal abscess with pain, fever, and evolving neurological deficit.
• Tethering presentation: the neuro-urological and orthopaedic features common to the group.

Imaging

• MRI of the whole spine to trace the tract, identify any intradural extension, and detect an associated dermoid or epidermoid; the bony level of the ostium can be misleading because tracts often ascend.
• Do not probe, cannulate, or inject contrast into the sinus; this risks introducing infection and is unnecessary when MRI is available.
• A high or atypical sacral pit, or one above the gluteal cleft, deserves particular scrutiny, in contrast to the common simple coccygeal pit.

Pathology & Molecular

Histology. Stratified squamous epithelium lining the tract; an associated dermoid or epidermoid cyst may be present at the termination.

Molecular. Sporadic; multifactorial.

Management

Surgery. Complete surgical excision of the tract from the skin to its termination, including any intradural component and inclusion cyst, with untethering of the cord and watertight dural closure. The tract is never simply ligated at the skin. When an abscess or established infection is present, antimicrobial therapy accompanies definitive excision.

Adjuvant therapy. Targeted antibiotics for established infection; ophthalmological/urological and rehabilitation input as dictated by any deficit.

Considerations. Plan to follow the tract intradurally; a tract that looks superficial externally may end at the conus. Incomplete excision leaves both the tethering and the infective risk.

Outcomes

Complete early excision before infection gives excellent results and removes both the tethering and the infective risk. Outcome after an established intraspinal abscess depends on the deficit incurred before treatment.

Epidemiology

Incidence

Rare; reported with a female predominance, and frequently associated with other dysraphic and cutaneous features.

Age peak

May present in infancy via cutaneous markers (a hairy patch overlying the lesion is characteristic) or later with tethered cord symptoms or scoliosis.

Location

Most commonly lower thoracic or lumbar; the septum lies between the hemicords at the level of the split.

Clinical Presentation

• Cutaneous markers are common, with a midline hypertrichotic patch over the lesion being characteristic.
• Tethered cord syndrome features (neuropathic bladder, lower-limb and foot changes, back/leg pain).
• Scoliosis is frequently associated and may be the presenting problem; a split cord should be sought before deformity surgery.

Imaging

• MRI of the whole spine defines the hemicords, the dural arrangement, and any tethering elements; CT best demonstrates a bony (Type I) septum.
• Determine the two typing features preoperatively: one dural tube versus two, and a bony/cartilaginous versus a fibrous septum.
• Screen for the associated tethering lesions (thickened filum, lipoma, dermal sinus) that frequently coexist.

Pathology & Molecular

Histology. Two hemicords; in Type I a dura-sheathed osseocartilaginous septum, in Type II a fibrous septum. The unified embryological mechanism invokes an adhesion between ecto- and endoderm with an accessory neurenteric canal and a bisecting endomesenchymal tract (Pang et al., 1992).

Molecular. Sporadic; multifactorial.

Management

Surgery. Microsurgical excision of the median septum and any associated dural sleeve, with untethering of the hemicords and correction of coexisting tethering elements at the same operation. Intra-operative neuromonitoring is used. In a child with scoliosis and a split cord, the split cord is generally addressed before, or concurrent with, deformity correction to avoid neurological injury from corrective traction.

Adjuvant therapy. Orthopaedic (scoliosis) and urological co-management.

Considerations. Type I and Type II differ operatively because of the septum and dural anatomy; accurate preoperative typing prevents surprises. Look deliberately for additional, commonly coexisting tethering lesions.

Outcomes

Untethering and septum excision arrest progression in most; established deficits tend to stabilise. Addressing the split cord before scoliosis correction reduces the risk of neurological deterioration during deformity surgery.

Split cord malformation; Pang Type I vs Type II

Epidemiology

Incidence

Radiological tethering is near-universal after myelomeningocele repair; symptomatic retethering requiring re-operation occurs in a minority and clusters around growth.

Age peak

Often during periods of rapid growth, including adolescence.

Location

At the site of the prior repair, where the placode adheres to the dorsal dura.

Clinical Presentation

• New or progressive deterioration is the hallmark: new back or leg pain, declining motor function, new sensory change, deteriorating bladder function on urodynamics, or a new or progressive scoliosis.
• The change is what matters; a stable long-standing deficit on a tethered-looking scan is not, by itself, an indication to re-operate.
• In a child with a shunt and a Chiari II malformation, exclude shunt malfunction and symptomatic hindbrain herniation as causes of new symptoms.

Imaging

• MRI documents the anatomy but cannot distinguish symptomatic from asymptomatic retethering; the diagnosis is clinical.
• Evaluate the whole picture: shunt function, hindbrain (Chiari II), and any syrinx, alongside the local tethering.
• Serial urodynamics is often the most sensitive objective marker of deterioration.

Pathology & Molecular

Histology. Fibrous scar binding the placode to the dura; arachnoid adhesions.

Molecular. Not applicable.

Management

Surgery. Re-untethering: microsurgical release of the placode from the dura and scar, which is more demanding than a primary repair because of distorted anatomy and adhesions. Expansile duraplasty may be used to enlarge the dural sac and reduce the cord-to-sac ratio. Intra-operative neuromonitoring is integral. Re-operation is reserved for genuine, documented deterioration.

Adjuvant therapy. Coordinated spina bifida multidisciplinary care; address shunt and Chiari issues on their own merits.

Considerations. Repeat untethering can itself be followed by further retethering; the indication should be clear clinical or urodynamic progression, and the family counselled about the possibility of recurrence.

Outcomes

Re-untethering for documented deterioration typically arrests progression and may relieve pain; reversal of established deficit is limited, and a proportion of children retether again over time.

Epidemiology

Incidence

A core elective operation of paediatric neurosurgery, performed across the substrate types covered in this module.

Age peak

Any age; timing is driven by symptoms (or, for some lesions, by the prophylaxis debate) rather than by a fixed age.

Location

Lumbosacral spine in the great majority.

Clinical Presentation

• Positioning and exposure: prone positioning, a midline incision, and a laminotomy/laminoplasty sufficient to reach normal dura above the lesion.
• Microsurgical dissection: identify and protect functioning neural tissue, follow the correct cleavage plane (the filum, the cord-lipoma interface, the septum, or the placode-dura scar), and untether the conus.
• Reconstruction and closure: reconstruct the placode where applicable, achieve a watertight dural closure (with duraplasty when needed to enlarge the sac), and close the muscle and fascia carefully to prevent CSF leak and pseudomeningocele.

Imaging

• Preoperative MRI (and CT for a bony split-cord septum) defines the anatomy and the operative plan.
• Postoperative MRI documents the new baseline; a degree of residual radiological tethering is expected and is not, by itself, a reason to re-operate.
• Retain the postoperative baseline imaging for comparison if later deterioration raises the question of retethering.

Pathology & Molecular

Histology. Substrate-dependent (see individual entries).

Molecular. Not applicable.

Management

Surgery. Intra-operative neuromonitoring is standard and central to safety: free-running and triggered electromyography of the lower-limb and sphincter muscles, the bulbocavernosus reflex to protect sacral function, and somatosensory and motor evoked potentials as indicated. Stimulation distinguishes the filum from a nerve root and helps map functional tissue within a lipoma or at a septum. Avoidance of a CSF leak is a defining technical goal: meticulous dural closure, often supplemented by a period of flat bed rest postoperatively.

Adjuvant therapy. Coordinated urology (peri-operative and follow-up urodynamics) and orthopaedics; physiotherapy as needed.

Considerations. Counsel families that the principal aim is to arrest progression; symptomatic improvement (especially of pain and recent bladder change) occurs in many but is not guaranteed, and retethering surveillance is lifelong, particularly after lipoma and re-do surgery.

Outcomes

Untethering arrests progression in the great majority of appropriately selected children, with low rates of new permanent deficit in experienced hands. Pain and recently acquired bladder dysfunction may improve; established motor deficit and fixed deformity usually stabilise rather than reverse.

By molecular subgroup: Retethering is most frequent after complex lipoma surgery and after re-do untethering, and least frequent after simple filum section. Techniques that achieve a low cord-to-sac ratio aim to reduce this risk (Pang et al., 2009).