Embryology of Spine n

spinal dysraphism

By Dr Viralkumar VasaniModerator: Dr Satish S

• Formation and separation of the germ layers

• Dorsal and ventral induction phases, and

• Phases of neurogenesis,

• Migration,

• Organization and

• Myelination.

• During week 1 (stages 2–4) the blastocyst is formed,

• During week 2 (stages 5 and 6) implantation occurs and the primitive streak is formed,

• Formation of the notochordal process and the beginning of neurulation (stages 7– 10).

• Somites first appear at stage 9. The neural folds begin to fuse at stage 10,

• Rostral and caudal neuropores close at stages11 and 12, respectively

Some Embryological fact

• first four embryonic weeks are also described as the period of blastogenesis,

• Fifth to eighth weeks as the period of organogenesis

• At the junction of trimesters 1 and 2, the fetus of about 90 days has a greatest length of 90 mm, whereas at the junction of trimesters 2 and 3, the

fetusis about 250 mm in length and weighs approximately 1,000 g

• Newborn brain weighs 300–400g at full term. Male brains weigh slightly more than those of females but, in either case, the brain constitutes 10% of the body weight

Beginning of NS• Gastrulation - birthday of the nervous system.

Time when

• 1)bilateral symmetry

• 2) three axes are established in the body of all vertebrates

• 3) Neuroepithelium can first be identified and distinguished from primitive germinal tissues

• Brain and spinal cord arise from an area of the ectoderm known as the neural plate.

• The folding of the neural plate, leading to successively the neural groove and the neural tube, is called primary neurulation.

• The caudal part of the neural tube does not arise by fusion of the neural folds but develops from the so-called caudal eminence. This process is called secondary neurulation

Stage Length Days External features

Internal Feature related to CNS

Stage Length Days External features

Internal Feature related to CNS

Primary Gastrulation• primitive streak (PS), midline structure, at the caudal end of the embryo

• Hensen’s node - cranial end of the primitive streak

• primitive groove, runs in the midline within the PS; the cranial end of the primitive groove is the primitive pit.

• cells of the epiblast migrate toward the PS and invaginate through the primitive groove. The first cells to ingress (while the PS is still elongating) are endodermal cells, which displace the hypoblast cells laterally and form prospective endoderm

• Displaced hypoblast cells form extraembryonic tissues.

• As the PS regresses, mesodermal cells ingress through the PS between the epiblast and newly formed endoderm and become the mesoderm.

• The remaining epiblast cells spread out to replace the cells that have ingressed through the primitive groove and thereby form both the neuroectoderm (the neural tube) and the cutaneous ectoderm (skin

Developing spinal cord

•

• Neural tube closure• Occurs craniocaudally from initial point of

contact• Initiated in region of cervical spinal cord (5

somite stage )• Posterior neuropore closes at day 25-27

(day 25 -27)• Posterior neuropore approximately located

at S2 level• Whole process known as neurulation

(primary neurulation )

Forces for neural tube formation

• Mesoderm appears to be important for orien- tation but not for closure of the neural tube.

• Expansion of the surface epithelium of the embryo is the principal extrinsic force for folding of the neuroepithelium to form the neural tube

• Intrinsic forces of the neuroepithelium, the cells of the floor plate have a wedge shape—narrow at the apex and broad at the base—that facilitates bending.

• The ependymal cells that form the floor plate are the first neural cells to differentiate, and they induce growth of the parenchyma of the ventral zone more than the dorsal regions

• mechanical effect may also facilitate curving of the neural placode (Flat plate).

• The direction of proliferation of new cells in the mitotic cycle, determined in part by the orientation of the mitotic spindle, becomes another mechanical force shaping the neural tube that is rostrocaudal orientation of most mitotic spindles

• Adhesion molecules

Role of Hensen’s Node

• as the “organizer” of the embryo.

• As the PS elongates, prospective endodermal cells within Hensen’s node migrate through the primitive pit.

• As the PS regresses, specialized mesodermal cells, prospective notochordal cells, migrate through the primitive pit and form the notochordal process in the midline between the neuroectoderm and endoderm.

• Notochord plays an imp role in directing subsequent neurulation.

• Between PODs 18 and 20, the notochordal process fuses (intercalates) with the underlying endoderm to form the notochordal plate. The notochordal plate is therefore incorporated into the roof of the yolk sac, with the notochordal canal becoming continuous with the yolk sac.

• Intercalation results in a direct communication, the primitive neurenteric canal, that connects the amnionic and yolk sacs at the level of Hensen’s node.

• The neurenteric canal persists for about 3 days, at the end of which the notochordal plate folds dorsoventrally and separates (excalates) from the endoderm and the neurenteric canal is obliterated.

• Thereafter, the true notochord exists as a solid rod of notochordal cells

Defination

Formation of neural tube

• Human neuroectoderm visible by day 16

• Pseudo stratified epithelium overlying the notochord

• Neural groove visible by day 17-19

• Neural folds (day 19 -21)

• Separate from the overlying ectoderm (dysjunction) and fuse to form the neural tube.

• The neural folds separate from the cutaneous ectoderm and fuse to form a closed neural tube between POD 21 and 23.

• Closure generally involves apposition and fusion of first the cutaneous ectoderm and then the neuroectoderm.

• The first part of the human neural tube to close is the region of the caudal rhombencephalon or cranial spinal cord, usually when five pairs of somites are present.

• Cranial neural tube closure may involve the coordinated interaction of as many as four waves of discontinuous neural tube closure.

• The spinal cord closes craniocaudally in a linear manner from the point of initial closure to the caudal neuropore.

• Cranial neuropore closes between POD 23 and 25, whereas the caudal neuropore closes between POD 25 and 27.

• Formation of neural crest• Neural crest cells originate at the

junction of surface ectoderm and neuroectoderm

• First visible on day 19-21• Continue forming till day 32

• Cranial neural crest cells contribute to the branchial arches and the arachnoid and pia mater of the cranium.

• spinal neural crest arises only after closure of the neural tube.

• Spinal neural crest cells undergo terminal differentiation into • melanocytes of the body wall and limbs, • Schwann cells investing the peripheral

nerves, • spinal cord meninges, • dorsal root and autonomic ganglion cells

of the spinal nerves• adrenal medulla.

• Secondary neurulation• Caudal cell mass extends from the posterior

neuropore to the cloacal membrane (day 25-27)• Pluripotent cells derived from the primitive

streak.• Contains neurons, neural crest cells and glial

cells and ependymal cells• The secondary neural tube is initially solid and

subsequently undergoes cavitation, eventually forming the tip of the conus medullaris and filum terminale by a process called retrogressive differentiation.

• Three processes are responsible for further development of the CCM• Condensation• Canalisation• Retrogressive differentiation

• Final derivatives• Distal sacral nerve roots,conus

medullaris,terminal ventricle,filum terminale and sacrococcygeal remnant

• Secondary neurulation continues till day 52

• Ascent of the conus medullaris• Process beginning day 43-48 and continuing

into post natal life probably• 2 distinct processes

• Retrogressive differentiation of the caudal neural tube (prior to day 54)

• Disparity between growth of spinal cord and vertebral column.

• Most rapid ascent between 8 to 25 weeks of gestation.

• At birth conus is at adult level of L1-L2 level.

• Low lying conus- below mid body of L2.

NTDs

• neural tube defects (NTDs), or localized failure of primary neurulation, that can arise through one of two mechanisms.

• The “nonclosure theory” proposes that NTDs represent primary failure of neural tube closure.

• The “overdistention theory,” introduced in 1769 by Morgagni and popularized by Gardner proposes that NTDs arise through overdistention and rupture of a previously closed neural tube.

Embryological classification Of Cong. dis

Spinal Dysraphism• Spinal dysraphism refers to a spectrum of disorders

in which there is defective midline closure of neural, bony, or other mesenchymal tissues.

• The “open” dysraphic states include myelocele, myelomeningocele, hydromyelia, Chiari II malformations, hemimyelocele, and myeloschisis.

• The closed dysraphic states include entities such as dermal sinus, lipomyelomeningocele, tight filum terminale, meningocele, myelocystocele, diastemato- myelia, neurenteric cyst, slit notochord, and developmental tumors such as spinal lipomas

Classification of Dysraphism

Spinal Dysraphism

Open

Myelomeningocele

MyeloceleHemi-MY/

MYME

Closed With S/C Mass

Lipomyelomeningocele

MeningoceleLipomyelocele

Myelocystocele

Terminal Myelocystocele

Closed without S/C Mass

Simple Dysraphic

state

Dermal Sinus

Intradural Lipoma

Complex Dysraphic

State

Diastometamyeli a

Neuroenteric cyst

Caudal Agenesis

Segmental Vertebral anamolies

Myelomeningoceles

• Disorder resulting from defective primary neurulation

• 98% of all Spinal dysraphism

• Incidence • 0.4 per 1000 live births• Racially variable

• 85% caudal thoraco lumbar spine, 10 % in the torax and the rest cervical

• 80-90 % associated with hydrocephalus and Chiari

• Trisomy 13 and trisomy 18

Associated defects • Brain stem defect includes

• Medullary kinking, tectal beaking, and intrinsic nuclei abnormalities

• Supratentorial abnormalities include • partial or complete dysgenesis of the corpus callosum,• polymicrogyria, a large massa intermedia, and gray matter

heterotopia.

• Mesodermal development of the skull • small posterior fossa, short clivus,• low-lying tentorium and torcular Herophili, wide incisura, and• enlarged foramen magnum. • Lückenschädel, or craniolacunia (scalloping of the skull

bones)

Cause of neuro-deterioration

• symptomatic hydrocephalus, • syringomyelia• Retethering of cord. • Chiari II malformation, Risk factors• mostly due to shunt malfunction resulting in

hydrocephalus

Patho Anatomy• Failure of neural tube closure results in an

exposed neural placode. The groove in the center of the placode is the remnant of the central canal.

• The spinal roots exit from the anterior surface of the placode such that the ventral roots lie medially and the dorsal roots lie laterally.

• The dura fuses with the defect in the fascia laterally. Functional neural tissue + either caudal to the placode or in the nerve roots exiting from the placode.

1. Axial schematic of myelomeningocele shows neural placode (star) protruding above skin surface due to expansion of underlying subarachnoid space (arrow).

2. Axial T2-weighted MR image in 1-day-old boy shows neural placode (black arrow) extending above skin surface due to expansion of underlying subarachnoid space (white arrow), which is characteristic of myelomeningocele.

MR Image of myelomeningocele

• Sagittal T2-weighted MR image from same patient with myelomeningocele shows neural placode (white arrow) protruding above skin surface due to expansion of underlying subarachnoid space (black arrow).

Clinical Examination• signs of myelopathy, including hyperreflexia and clonus, because they

often have an incomplete functional spinal cord transection in 2/3rd

• sensory level by stimulus - distally to proximally until the infant grimaces.

• A stimulus is applied above the sensory level, and the distal-most voluntary motion seen for motor level determination

• With an L1-3 level, the infant has hip flexion with extended knees and clubfeet.

• The presence of intact hip adduction, hip flexion, and knee extension with inverted feet is indicative of an L2-4 level.

• With an L5-S2 level, the infant has hip adduction, knee extension, and knee flexion with dorsiflexed feet.

• Infants with a sacral level may appear intact except for weakness of plantar flexion and rocker-bottom feet.

• A flaccid pelvic floor and patulous anus are often present

• Prenatal diagnosis• Maternal serum Alpha feto protein : initial

screening test• High resolution fetal ultrasonography.

• Can also demonstrate hydrocephalus and Chiari II abnormality (lemon and banana sign)

• Amniocentesis : if MSAFP and USG are suggestive • Ach esterase levels along with AFP

• AFP can increase in other developmental anomalies of the gut and kidneys.

“lemon sign” Normal fetal head

D/D

• At least 22 other fetal abnormalities besides myelomeningocele increase MSAFP levels.

• Abdominal abnormalities such as omphalocele, cloacal exstrophy, esophageal atresia, annular pan- creas, duodenal atresia, and gastroschisis and

• urologic abnormalities such as congenital nephrosis, polycystic kidneys, urinary tract obstruction, and renal

• sacrococcygeal cystic teratoma

Preop evaluation- Clinical

• General• Repaired within 72 hrs• Enteral feeding avoided to prevent fecal soiling

of placode• Prone position ,saline dressings

• Neurosurgical• Sensory level determined • Motor evaluation – distal most voluntary motion

evaluated. Limb abnormalities documented.• Anal tone and anal reflex evaluated

• Ventricular size documented with preop USG and NCCT head.

• Imaging study shows that differentiating feature between a myelomeningocele and myelocele is the position of the neural placode relative to the skin surface

• The neural placode protrudes above the skin surface with a myelomeningocele and is flush with the skin surface with a myelocele

• Observe for symptoms of Chiari II

• Renal evaluation• 90 % have neurogenic bladder.• All should have preop Renal ultrasound for detecting

severe anomalies.

• CIC if fails to void.

Myelocele

1. Axial schematic of myelocele shows neural placode (arrow) flush with skin surface.

2. Axial T2-weighted MR image in 1-day-old girl shows exposed neural placode (arrow) that

is flush with skin surface, consistent with myelocele. There is no expansion of underlying subarachnoid space.

Repair• Timing of repair:

• Myelomeningocele repair can be performed safely up to 72 hours after birth

• Delayed repair – Increases chance of ventriculitis by 5 times,

• shunt infection developed in about 75%, and the mortality was 13%

• In case Delay • 1) Cultures from the neural placode – No growth – go ahead

n repair• If infection +, -external ventricular drainage and appropriate

antibiotics until the infection clears – Then repair

• Shunt before repair – High chance of shunt inf./ Meningitits – IQ impairment (due to inf)

• PREPARATION • Intraoperatively avoid hypothermia, hypovolemia, and

hypoglycemia. • A doughnut-shaped sponge - to protect the myelomeningocele

while intubation.

• If severe Hydrocephalus - CSF diversion before closure of the myelomeningocele - to minimize pressure on the myelomeningocele dural closure

• entire back and flanks are prepared and draped to facilitate extensive closure if needed.

• Contact between povidone- iodine solution and the neural placode should be avoided

• purposes of myelomeningocele repair are to protect the functional spinal cord tissue, prevent loss of CSF, and minimize the risk for meningitis by reconstructing the neural tube and its coverings.

• The margin between the arachnoid of the neural placode and the dystrophic epidermis, or the junctional zone, is the site of the initial incision.

• The goal is to free the neural placode from the surrounding junctional zone circumferentially.

• Duraplasty with thoracolumbar fascia or another dural substitute is performed when necessary to prevent leakage of CSF.

Post op care

• Post op antibiotics

• Prevention of fecal contamination of wound

• Nurse in Trendlenberg’s

• Observe for Hydrocephalus – shunt if HCP present

• Complications• Superficial wound dehiscence• Meningitis

• Symptomatic chiari • Ensure functioning shunt• Hindbrain decompression

Prognosis• 10 to 15% succumb <6yr of age even with Multi specialty

aggressive approach

• >95% Lives >2 years

• 8 to 17 % will have urinary control rest on Drugs / CIC

• >87% will have social fecal incontinence

• L3 function allows one to stand erect, and L4 and L5 function allows ambulation – During the first decade, approximately 60% of children with spina bifida are community ambulators, without or with assistive devices (including wheelchairs) – Reduces to 17% in teenagers

• IQ stays N if no inf. – only <10% economically independent

Occult spinal dysraphism

• Aka Closed dysraphism

• Of 2 types ; with/without s/c mass

• Congenital spinal defects covered by intact skin

• Causative lesions• Fatty filum terminale• Lipomyelomeningocele• Split cord malformations type I and II• Inclusion lesions (dermoid, dermal sinus tract)• Neurenteric cyst• Myelocystocele

Closed / Occult type• Closed With S/C Mass

• Lipomyelomeningocele

• Meningocele

• Lipomyelocele

• Myelocystocele

• Terminal Myelocystocele

• Closed without S/C Mass

• Simple Dysraphic state

• Dermal Sinus

• Intradural Lipoma

• Complex Dysraphic State

• Diastometamyelia

• Neuroenteric cyst

• Caudal Agenesis

• Closed Spinal Dysraphisms With a Subcutaneous Mass

1. Lipomas with a dural defect—• include both lipomyeloceles and lipomyelomeningoceles. • result from a defect in primary neurulation whereby mesenchymal tissue enters

the neural tube and forms lipomatous tissue. • characterized clinically by the presence of a subcutaneous fatty mass above the

intergluteal crease. • The main differentiating is the position of the placode–lipoma interface. With a

lipomyelocele, the placode–lipoma interface lies within the spinal canal where as it is outside of the spinal canal in case of lipomyelomeningocele, it lies due to expansion of the sub arachnoid space .

2. Meningocele—Herniation of a CSF-filled sac lined by dura and arachnoid mater is referred to as a meningocele. The spinal cord is not located within a meningocele but may be tethered to the neck of the CSF-filled sac.

• Posterior meningoceles herniate through a posterior spina bifida (osseous defect of posterior spinal elements) and are usually lumbar or sacral in location but also can occur in the occipital and cervical regions.

• Anterior meningoceles are usually presacral in location but also can occur elsewhere

Manifestations of occult spinal dysraphism

Cutaneous stigmata Orthopedic deformities

Urologic problems

Asymmetric gluteal cleft

Foot or leg deformities

Neurogenic bladder

Capillary hemangioma

Scoliosis UTIs

Subcutaneous lipomas

Sacral agenesis Incontinence

Hypertrichosis Delay in toilet training

Dermal sinus tract

Cutis aplasia

Neurological signs and symptoms in different age

groupsInfants Toddler Older children Young adults

Decreased spontaneous leg movements

Delayed walking Asymmetric motor/ sensory development

Back pain

Absent reflexes Abnormal gait Back/leg pain Leg cramping/pain

Leg atrophy UMN signs Spasticity

Foot asymmetry Painless ulceration

Hyperreflexia

Decreased urinary stream

Bowel/bladder incontinence.

Structure Findings

Lamina Fusion defects,midline defects,abnormal spinous processes

Vertebral bodies Hemivertebrae, Butterfly vertebrae, Block vertebrae, Midline cleft defects, canal stenosis

Disk space Congenital narrowing

Pedicles Flattening, thinning

Widening of spinal canal Interpedicular widening, scalloping of posterior border, Midline bony spur.

Failure of development Reduced number of vertebral bodies, Absence of parts of vertebrae, sacral dysjunction

Spinal curvature Scoliosis, kyphosis, lordosis.

Lipomyelomeningoceles

• Lipoma tethering the cord to the subcutaneous tissue

• Fascial, spinous and dural defect• Lipoma cord interface distracted out of

the spinal canal by traction created by tethering

LMMCAxial schematic of lipomyelomeningocele shows placode–lipoma interface (arrow) lies outside of spinal canal due to expansion of subarachnoid space.

Axial T1-weighted MR image in 18-month-old boy shows lipomyelomeningocele (arrow) that is differentiated from lipomyelocele by location of placode–lipoma interface outside of spinal canal due to expansion of subarachnoid space.

LMC- Lipomyelocele

• Axial schematic of lipomyelocele shows placode–lipoma interface lies within spinal canal.

• Axial T2-weighted MR image in 3-year-old girl shows placode–lipoma interface within spinal canal, characteristic for lipomyelocele.

Lipomyelocele

Sagittal T1-weighted MR image in 3-year-old girl with lipomyelocele shows subcutaneous fatty mass (black arrow) and placode–lipoma interface (white arrow) within spinal canal.

Chapman’s classification of LMM

• Classification• Type I (dorsal lipoma)• Type II (transitional lipoma)• Type III ( terminal lipoma)

• Dorsal lipoma (Type I)• Fibrolipomatous stalk tethering cord

proximal to conus• Usually at middle lumbar to lumbo sacral

level• Dorsal spinal cord dysraphic at site of

attachment of lipoma• Site of attachment medial to the dorsal root

entry• Normal spinal cord distal to myeloschisis.• Roots lie within the subarachnoid space.

Dorsal lipoma

• Caudal or terminal lipomas (type III)• Directly from conus medullaris or filum

terminale• Largely or wholly intradural• Nerve roots entangled in the lipoma• Lipoma cord interface caudal to the

dorsal root entry zone.• Filum may be fatty, thickened and

sometimes attached to subcuatneous tissue ( sacral dimple).

Terminal lipomas

• Transitional lipomas• Share the charcteristics of both Type 1

and type 2.• No normal spinal cord distal to lipoma

attachment• Initially dorsal roots may be separate

but caudally become enmeshed into the lipoma.

• Frequently assymmetric attachment to cord.

Transitional lipomas

Abnormal embryology LMM

• Usually a disjunction in timing of neural tube closure and cutaneous ectoderm closure

• Elements of the ectoderm become incorporated into the incompletely closed neural tube.

Clinical features

• Subcutaneous masses over the back

• Stigmata of occult dysraphism• Hypertrichosis• Hemangioma• Hypo/ hyperpigmented patch• Dermal pit or sinus • Atretic meningocele• Assymmetric gluteal cleft

• Inexorable symptomatic progression - in untreated cases

• Risk of precipitous neurologic deterioration• Orthopedic syndrome

• Limb length discrepancy, high pedal arches, hammer toes, calcaneovarus/ valgus foot deformity.

• Urologic syndrome• Urinary incontinence, post void dribbling,

urgency, frequency

• Intractable pain in the legs, back, pelvis or perineum.

Indication for surgical repair

• Asymptomatic infant older than 2 months

• Presence of orthopedic, pain or urologic syndrome

• Neurological symptoms

• Prior to corrective spinal surgery.

Principal Goal of surgery

• Detethering of spinal cord• Decompression of the cord by removing as much

lipoma as possible• Reconstruct the spinal cord and dural sac• Preservation of the functional tissue

• Surgical principles• Relationship between the lipoma-cord interface

and dorsal roots to be established• Conservative excision of the lipoma to avoid

injury to the cord/ exiting roots.

• Complications of surgical repair• Early – CSF leak/ pseudo meningoceles & New

Neurological deficit• Late – retethering of the cord

• Mostly presenting between 3-8, 11-22 months after surgery

• Upto 20% cases may demonstrate retethering• Diagnosis primarily clinical.

• Aseptic meningitis from host-graft inflammation• meningitis, • Intradural abscess, • wound infection, and wound breakdown

Lipoma of the terminal filum

Less severe form of Occult SD

More than 2 mm thickness of the filum on MR imaging

Frequently assosciated with sacral/gluteal cleft dimples.

May be associated with VATER association, imperforate anus, cloacal extrophy and other urogenital abnormalities.

Sometimes a/w sacral agenesis

Reflects defective secondary neurulation

Clinical presentation Orthopedic Urologic Pain

All asymptomatic infants and symptomatic adults are surgical candidates.

Surgical procedure is the exposure of filum through lumbosacral laminectomy or interlaminar approach The filum identified separated from nerve roots

and cut.

Closed SD without S/C Mass

• Closed without S/C Mass

• Simple Dysraphic state

• Intradural Lipoma

• Filar lipoma,

• Tight filum terminale,

• Persistent terminal ventricle

• Dermal Sinus

• Complex Dysraphic State

• Diastometamyelia

• Neuroenteric cyst

• Caudal Agenesis

• Segmental Vertebral anamolies

• An intradural lipoma - a lipoma located along the dorsal midline that is contained within the dural sac. No open spinal dysraphism is present.

• M.C site: lumbosacral - present with tethered cord syndrome, a clinical syndrome of progressive neurologic abnormalities in the setting of traction on a low lying conus medullaris.

• Fibrolipomatous thickening of the filum terminale is referred to as a filar lipoma. On imaging, a filar lipoma _ - Normal variant if there is no clinical evidence of tethered cord syndrome

• Tight filum terminale is characterized by hypertrophy and shortening of the filum terminale causing tethering of the spinal cord and impaired ascent of the conus medullaris. The conus medullaris is low lying relative to its normal position that is above the L2–L3 disc level.

• Persistence of a small, ependymal lined cavity within the conus medullaris is referred to as a persistent terminal ventricle.

• Location immediately above the filum terminale and lack of contrast enhancement, which differentiate this entity from other cystic lesions of the conus medullaris.

Intra dural Lipoma

Complex dysraphic states

divided into two categories:

• disorders of midline notochordal integration • dorsal enteric fistula • neurenteric cyst• Diastematomyelia

• disorders of notochordal formation, which include • caudal agenesis and • segmental spinal dysgenesis

• Diastematomyelia—Separation of the spinal cord into two hemicords. The two hemi cords are usually symmetric, although the length of separation is variable.

• two types of diastematomyelia.

• In type 1, the two hemicords are located within individual dural tubes separated by an osseous or cartilaginous septum.

• In type 2, there is a single dural tube containing two hemi cords, sometimes with an intervening fibrous septum. Diastematomyelia can present clinically with scoliosis and Tethering

Split cord malformation

• Longitudinal developmental splitting of the cord over one or multiple levels

• Two types:

• Both types may be present simultaneously at different levels

Type I malformations (formerly diastematomyelia) are characterized by a bony septum that cleaves the spinal canal in the sagittal plane and a duplicated thecal sacType II malformations (formerly diplomyelia) are characterized by a cleft cord within a single dural sac, often tethered by a fibrous midline septum to the adjacent dura (single dural sheath, hemicords separated by fibrotic bands

Split cord Malformation

• Exceedingly rare

• Represent 3.8% to 5% of all congenital spinal anomalies.

• prevalence of SCM to be 1 in 5000 (0.02%) live births.

• slight female preponderance, approximately 1.3:1.7

• The peak age is 4 to 7 years,

• second peak between 12 and 16 years - post pubescent growth spurt.

• Type I SCMs > type II lesions

Pang’s theory of embryogenesis

Unifide theory • Pang - unified theory - type I and type II SCM to

a single error in embryogenesis:

• Formation of abnormal fistula through midline embryonic disc that maintains communication b/w Yolk sac & amniotic cavity contact b/w ecto + Endoderm

• This fistula causes splitting of Notochord & overlying neural plate- mostly rostral to henson’s node

Associated Anomaly• Tethered/low-lying cord (>50%),

• Kyphoscoliosis (44% to 60%),

• Syringomyelia (27.5% to 44%), and

• Spina bifida (11% to 26%)

Clinical signs - symptoms

• “faun’s tail,” consists of a patch of unusually coarse, raised hair - strong association with type I SCM.

• Capillary hemangioma underlying these hairy patches.

• Nearly 50% of patients have gross (i.e., structural) asymmetry of the lower extremities-- neuro-orthopedic syndrome.

• characterized by a triad of 1. limb length discrepancy, 2. muscular atrophy (resulting in secondary weakness), and 3. clubfoot deformity (talipes equinovarus).

• The smaller limb is often ipsilateral to a smaller hemicord.

MRI Findings

• MRI Spine shows 1. presence of two hemi cords, on T1-w sequences. 2. demonstrating the presence of an associated fatty filum, affect

one or both hemicords, a dermal sinus tract, or a terminal lipoma.

• Associated tethering anomalies are present in approximately half of all patients and in more than 90% of those with a low-lying conus.

• T2-weighted MRI for 1. categorization of the malformation as type I or type II . 2. hypointense fibrous band in type II SCM.

3. To demonstrate syringomyelia proximal to the cleft, which may extend into one or both hemicords

Type 1 & Type 2 SCM MRI

MGTMNT

• 85% of patients without intervention suffer from a progressive neurological deficit versus only 4.5% after surgical treatment

• Pang too suported prophylactic surgery in Type 1 malformation.. Whereas in Type 2 both- some – W&W policy

• Surgery – careful – incision 1 to 2 level more exposure

Operative

• Operative management• Surgical detethering of cord by excision of the bony

spur/ division of the fibrous bands• Avoid damage to the hemi cords during excision of

the spur.• For type I SCM, the initial laminectomies should be

limited to adjacent levels while initially avoiding exposure of dura at the level of the midline bony spur.

• Rongeurs or a high-speed drill (or both) - to perform bilateral paramedian laminectomies ( preserve the midline lamina and spinous process to prevent any torque or lateral force from disrupting the bony spur prematurely.)

• Careful when removing lamina at the level of the SCM in type II malformations because of the frequent presence of transdural adhesions - most commonly attached dorsally but ventrally too. Often, the dura at this level grossly abnormal.

• All non-neural and non- functional adhesive bands should be transected, beginning dorsally and then gently rolling the hemicords to one side and transecting any ventral attachments

• Hemicords are typically closely approximated with no clear intervening plane. Resection of the fibrous band within the split spinal cord itself is not indicated.

• Any associated tethering lesion (sinus tract, fatty filum, or terminal lipoma) should also be addressed

Outcome & Complication Of SCM

Secondary repair of an SCM in a patient with a previously closed myelomeningocele at the same level - failed wound healing as high as 10%

Neurenteric cysts

• Persistent neurenteric canal communicating between yolk sac and amniotic cavity

• Intradural, extramedullary mucosa lined cysts

• Formed from persistents tracts communicating with respiratory and gut epithelia.

• Neurenteric cysts represent a more localized form of dorsal enteric fistula.

• These cysts are lined with mucin secreting epithelium similar to the GIT and located in the cervicothoracic spine anterior to the spinal cord

• Associated with vertebral anomalies

• MRI- demonstrates non- contrast enhancing intradural extramedullary cyst

• Presentation usually in late years (50-60 years)

• May also present in pediatric age group

• Most common location is cervico- thoracic

• Usually postero-lateral surgical approach

• Complete excision of cyst – long term symptom free survival.

Dermal sinus tracts

Abnormal tracts communicating between the skin and intraspinal compartment.

Most common- lumbosacral location

May occur anywhere from nasion to coccyx in midline

May be accompanied by other cutaneous stigmata.

Tract terminates within thecal sac mostly

Half may have associated dermoids, epidermoids, teratoma at termination.

• Potential pathway for spread of infection

• Repeated episodes of meningitis with atypical organisms

• Operative repair consists of complete excision of the track under prophylactic antibiotic cover.

• Gram positive and gram negative coverage

Meningoceles

• Distinguished from MMCs by absence of hydrocephalus , chiari malformation or lower limb abnormalities

• Dural defect through which CSF space and meninges herniate.

• Concomitant neurocutaneous lesions such as lipomas, dermal sinus tracts may cause tethering

• Surgical repair of defect at 4-6 months of age.

Posterior meningocele

Anterior meningocele

• Herniation of meninges and CSF in ventral location

• Commonly in presacral and lumbosacral region

• Female predominance• Currarino’s triad- anorectal abnormalities,

presacral mass, sacral bony abnormalities.• Presacral tumour may be epidermoid,

dermoid or teratoma• Meningitis by atypical organisms may also

occur.• Repair the dural defect and detether the

cord.

Anterior meningoceles

myelocystoceles

• Terminal dilatation of the central canal that herniates through defective posterior elements

• Expanded spinal cord, CSF, fibrous bands and meninges and lipomatous elements

• Result from disordered development of the caudal cell mass

• Associated anomalies of the anorectal system, lower GI tract and spinal column

Myelocystocele

Herniation of dilated central canal through posterior spinal defect.

Terminal Myelocystocele

Terminal myelocystocele—Herniation of large terminal syrinx (syringocele) into a posterior meningocele through a posterior spinal defect. The terminal syrinx component communicates with the central canal, and the meningocele component communicates with the subarachnoid space. The terminal syrinx and meningocele components do not usually communicate with each other.

• Surgical repair attempted because of the resultant tethering of spinal cord.

• Per-op trumpet shaped distended conus often adheres to the superficial fat

• Detethering may be difficult.

Thank you