11. ANOMALIES OF GASTRULATION
Failure Of Notochord Formation:
Caudal Regression Syndrome (CRS)/Caudal Agenesis
Segmental Spinal Dysgenesis
Anomalies Of Notochord Induction:
Process of fusion of paired notochordal anlage to form a
single midline notochordal process is called midline
notochordal integration.
Any abnormality at
this stage results in longitudinal splitting of spinal cord
lead to split notochord syndromes:
1.Neurenteric cyst and dorsal-enteric spinal anomalies
2.Diastematomyelia
13. CRS
2 types.
Type 1:
Both caudal cell mass and notochord formation is affected high position (most
commonly at the level of D12 vertebra) and wedge shaped conus medullaris.
Accompanying varying degree of vertebral aplasia (usually L5 through S2).
Associated with severe visceral and orthopedic anomalies.
14. CRS
Type 2:
Normal primary neurulation with defective secondary neurulation
Abnormal development of only caudal cell mass with unaffected true notochord
formation.
Only the most caudal part of conus medullaris is absent in type II CA.
Vertebral dysgenesis is less severe and patients present with tethered cord syndrome as
the conus in these cases is stretched and tethered.
15. CRS
In general, the higher the cord termination, the more severe is the sacral anomalies.
The most severe CRS presentations are lumbosacral agenesis in which the spine terminates at the lower
thoracic level and there is severe sacral dysgenesis with fused lower extremities (sirenomyelia).
Associations:
VACTERL
Currarino syndrome
Split cord malformations
17. Segmental Spinal Dysgenesis
Very rare clinico-radiological entity characterised by:
Congenital pareparesis or paraplegia +
Congenital lower limb deformities+
Segmental thoracolumbar or lumbar vertebral dysgenesis or agenesis - congenital thoracic or
lumbar kyphosis with a palpable dorsal bone spur located at the gibbus apex.+
Segmental thoracolumbar or lumbar spinal cord dysgenesis or agenesis; The upper spinal cord is
normal, however, the cord segment below the dysgenetic segment is bulky, thickened and low-
lying.
The spinal canal proximal and distal to the dysgenetic level is of normal calibre.
18.
19. Neurenteric Cyst (NEC)
Consists of an intraspinal cyst lined by enteric mucosa.
Most common: Thoracic spine > cervical spine.
Arise from an abnormal connection between primitive endoderm and ectoderm that persists
beyond the third embryonic week.
Normally, the notochord separates ventral endoderm (foregut) and dorsal ectoderm (skin, spinal
cord) during embryogenesis
20. Neurenteric Cyst (NEC)
In NEC, a separation failure “splits” the notochord and hinders the development of mesoderm,
which traps a small piece of primitive gut within the developing spinal canal.
This gut remnant may become isolated forming a cyst or it may maintain connections with gut or
skin (or both) fistulas or sinuses.
Neurenteric cyst - anterior to spinal cord with adjacent vertebral anomalies.
Typically extramedullary intradural compartment - iso- to hyperintense to CSF on both T1 and T2
weighted images due to high protein content and show absent contrast enhancement.
21.
22. Diastematomyelia
Most common form of defective midline notochordal integration.
Due to defective midline integration there are two notochordal
processes each of which induces formation of separate neural plate
with intervening primitive streak tissue.
Separation of the spinal cord into two hemicords.
A hairy tuft on the patient’s back can be a distinctive finding on
physical examination.
Can present clinically with scoliosis and tethered-cord syndrome.
Associated with vertebral anomalies and hydromyelia
23. Diastematomyelia
The development of the primitive streak
tissue decides the type of
diastematomyelia.
Type 1: Intervening primitive streak
develops into bone or cartilage 2
hemicords in different dural sacs
separated by an osteocartilaginous
septum
24. Type 2: The primitive streak is
reabsorbed or forms a fibrous septum
2 hemicords lie within the same dural
sac sometimes with an intervening
fibrous septum.
25. ANOMALIES OF PRIMARY
NEURULATION
Anomalies Of Premature Dysjunction
Premature dysjunction Perineural
mesenchyme gets interposed between
neural tube and ectoderm may
differentiate into fat and prevent
complete neural tube closure
1. Lipomyelocele (LMC)
2. Lipomyelomeningocele (LMMC)
3. Spinal Lipoma
Anomalies Of Non-Dysjunction
Failure of dissociation of neural tube
from adjacent cutaneous tissue
(Nondysjunction) an ectodermal–
neuroectodermal tract formtion
prevents mesenchymal migration
open neural tube defect spectrum:
1. Dorsal dermal sinus
2. Myelomeningocele (MMC) and
myelocele
26. LMC & LMMC
20–56% of occult spinal dysraphism and
20% of skin-covered lumbosacral
masses.
Clinically characterized by the presence
of subcutaneous fatty mass lesion above
the intergluteal line which may extend to
buttocks.
LMMC vs LMC:
◦ Based on position of the position of the neural
placode–lipoma interface.
◦ In LMC: placode–lipoma interface lies within
or at the edge of the spinal canal.
◦ In LMMC: placode–lipoma interface lies
outside of the spinal canal due to expansion of
the sub-arachnoid space
◦ In LMMC there is expansion of subarachnoid
space anterior to the cord pushing the neural
placode - lipoma interface posteriorly to lie
outside the boundaries of spinal canal.
27. Lipoma placode interface in
lipomyelocele and
lipomyelomeningocele. Axial T2
weighted images in cases of
lipomyelocele (A) and axial T1 weighted
images in case of lipomyelomeningocele
(B) showing high intensity fat on the
dorsal aspect of the neural placode which
is continuous with the adjacent
subcutaneous fat. The lipoma placode
interface (black arrow) is within the spinal
canal in lipomyelocele and outside the
spinal canal in lipomyelomeningocele.
Both these conditions have intact skin
covering.
28. Lipomyelocele. T2 weighted sagittal (A), T1 weighted sagittal (B) and T2 weighted axial (C) images of lumbosacral
spine in a case of lumbar lipomyelocele. High intensity fat is seen on the dorsal aspect of the neural placode which is
continuous with the adjacent subcutaneous fat (arrowhead) through an open defect in the posterior aspect of spinal
canal. The placode lipoma interface is within the spinal canal (arrow).
29. In both cases, syringomyelia is a
commonly associated finding.
In hemilipomyelocele or
hemilipomyelomeningocele there is
associated diastematomyelia with one
of the hemicord showing lipomyelocele
or lipomyelomeningocele respectively
30. Hemilipomyelomeningocele. T2 weighted sagittal (A), T1 weighted sagittal (B), T2
weighted axial (C) and T1 weighted axial (D) images in a case of
hemilipomyelomeningocele. There is diastematomyelia with bony septum (white arrow)
suggestive of type I diastematomyelia. There is defect in the posterior spinal canal on
the right side through which the spinal canal contents herniate with intact overlying skin
and subcutaneous tissue (arrowhead). There is expansion of
subarachnoid space (+) anterior to the cord pushing the neural placode - lipoma
interface posteriorly to lie outside the boundaries of spinal canal (arrow).
31. Intradural Lipoma
Lipoma located along the dorsal
midline and contained within the dural
sac.
No open spinal dysraphism
Most commonly lumbosacral in
location.
Associated with TCS
32. Dorsal Dermal Sinus Tract (DST)
Epithelial lined fistulous communication between CNS or its meningeal covering and skin.
Results from focal incomplete disjunction between neuroectoderm and cutaneous ectoderm.
Clinically: Midline dimple or ostium on the cutaneous surface
The true congenital dorsal DST usually has an atypical dimple at the ostium that is large (>5mm), often
asymmetric and remote (>2.5cm) from the anus.
(These features help distinguish the dermal sinus from its clinically asymptomatic mimic,
simple coccygeal dimple.)
33. DST
Most common: Lumbosacral spine >
occiput.
Commonly associated with cutaneous
stigmata of underlying occult spinal
dysraphism like hairy nevus,
hemangioma or hyperpigmentation.
In all cases, there is some degree of focal
dysraphism, which may be as subtle as a
bifid spinous process.
The sinus tract/cord is epithelial-cell lined
and may or may not be canalised.
When patent, it exposes the patient to an
elevated risk of meningitis.
30–50% of DSTs may have an associated
dermoid or epidermoid cyst
35. MMC & Myeloceles
OSD – i.e., the neural placode is exposed through a midline skin defect on the back.
Defective closure of the primary neural tube OSD
OSD usually involves the lower lumbar and sacral regions (98%).
Rare in cervical and upper thoracic spine, probably because the lesion in these areas are
more severe leading to fetal demise
Most common OSD = Myelomeningoceles (>98%).
Myelomeningocele - Amost always seen in the context of a Chiari 2 malformation.
36. MMC & Myeloceles
Myeloceles - Rare.
Usually diagnosed clinically - Neonate presents with a midline reddish exposed neural
placode
Myelomeningocele vs myelocele:
◦ Based on position of the neural placode relative to the skin surface.
◦ In myelomeningocele - both the neural placode and meningeal lining protrude through the
bony and cutaneous defect in the midline
◦ In myelocele - the neural placode is flush with the skin surface
37. Lumbar myelomeningocele. T2 weighted sagittal (A), T1 weighted sagittal
(B) and T2 weighted axial (C) images of lumbar spine showing
myelomeningocele. There is posterior herniation of a CSF filled sac (white
arrows) containing cord and nerve fibers (black arrows). There is absence
of skin covering with interruption of subcutaneous fat.
Myelocele. Axial T2 weighted (A) and sagittal T1 weighted (B) images of
dorsolumbar spine in a case of myelocele showing the neural placode
(arrowhead) flush with the skin surface (arrow). Skin covering is absent
over the myelocele.
38. Fetal Myelomeningocele with Chiari II malformation. Axial (A) and sagittal (B) T2 weighted images of lumbar spine of fetus showing splaying of
posterior elements of lumbar vertebrae with herniation of spinal canal contents (black arrow) suggestive of MMC. Axial T2 weighted image of brain
(C) shows associated hydrocephalus. Hydrocephalus in the setting of MMC in a fetus is considered highly suggestive of Chiari II malformation.
39. MMC & Myeloceles
Now mostly detected on prenatal USG.
Management - Surgical repair.
In-utero repair – 2nd trimester
Preserves neurologic function,
reverses/arrests the changes of Chiari II
malformation and reduces the need for
postnatal ventriculoperitoneal shunt
40. COMBINED ANOMALIES OF GASTRULATION &
PRIMARY NEURULATION
Hemimyelomeningocele and
hemimyelocele
Extremely rare.
Occur when a myelomeningocele or
myelocele is associated with
diastematomyelia and one hemicord fails
to neurulate
One of the two hemicords exhibits a
myelomeningocele or myelocele while the
other hemicord can be normal or is
tethered
41. ANOMALIES OF SECONDARY NEURULATION
Failure of expected secondary neurulation leads to conditions such as :
1. Low Lying Cord
2. Tethered Cord Syndrome
3. Persistent Terminal Ventricle/Fifth Ventricle.
4. Intrasacral – Anterior Sacral Meningocele
5. Terminal Myelocystocele
6. Lipoma of filum terminale.
It is also implicated in pathogenesis of caudal regression syndrome and segmental spinal dysgenesis.
42. Low Lying Cord
Persistent cord termination
below L2-L3 after the first
month of life in a full-gestation
infant is abnormally low-lying.
Axial T1-weighted images are
most accurate in determining the
conus level.
43. Tethered Cord Syndrome (TCS)
Most likely present during periods of rapid somatic growth.
Manifests clinically as gait spasticity, low back and leg pain that is worse in the
morning, lower extremity sensory abnormalities and/or bladder difficulties.
On imaging, TCS strictly refers to patients with a low-lying cord and thickened filum
(> 1.5mm) that is tethered to the dural sac.
44. TCS
Causes of tethered cord syndrome:
1. Closed spinal dysraphisms in the spectrum of spinal lipomas (lipomyelomeningocele,
conus lipoma, and filar lipoma)
2. Arachnoid adhesions (due to trauma/surgery or infection/inflammation)
3. Split cord malformation (diastematomyelia and diplomyelia)
4. Dermal sinus tracts
5. Dermoid/epidermoid tumors
Tight filum terminale syndrome is a subtype of the tethered cord syndrome that is
attributed to a thick, short, and/or otherwise inelastic filum terminale rather than
other tethering agents
45.
46. Persistent Terminal Ventricle/Fifth Ventricle.
By day 48, a transient ventriculus terminalis appears in the future conus.
Incomplete regression of terminal ventricle during the stage of retrogressive differentiation in secondary
neurulation is responsible for the condition
A 5th ventricle not accompanied by other pathologies is a frequent finding that does not have
pathological significance during the first 5 years of life.
Key imaging features include location immediately above filum terminale and lack of contrast
enhancement which differentiates this entity from other cystic lesions of the conus medullaris
47. Meningocele
Meningocele Herniation of CSF filled sac lined by dura and arachnoid mater.
Intrasacral meningocele Within an enlarged sacral spinal canal - CSF flows from the
tip of the subarachnoid space into the meningocele by a pedicle attached to the caudal
termination of the dural sac.
Anterior meningoceles - Usually presacral in location - has a large anterior outpouching
that traverses an enlarged sacral foramen and produces a presacral cystic mass.
Posterior meningocele Due to herniation of meningial lining through posterior spina
bifida - usually lumbosacral in location but can be seen in other locations also.
48. Meningocele
Exact embryogenesis - unknown - Thought to be caused by ballooning of meninges due to CSF
pulsation.
By definition, spinal cord should not be seen within the meningocele but may be seen tethered to its
neck.
Meningocele may contain nerve roots and or filum terminale which usually appear hypertrophied.
Associations:
i. Sacral vertebral anomalies
ii. Diastematomyelia
iii. TCS.
iv. Most ASMs are sporadic but a minority show an inherited predisposition within the Currarino triad or in
syndromes that feature dural dysplasia, such as NF1 and Marfan syndrome
49.
50.
51. Filar Lipoma
Fibrolipomatous thickening of the filum
terminale.
Appears hyperintense on T1 and T2 weighted
images within a thickened filum terminale.
1.5% - 5% of normal adult population may
show fat within filum – so can be considered a
normal variant if there is no clinical evidence of
tethered-cord syndrome
52. Terminal Myelocystocele
Herniation of a large terminal synrinx
(syringocele) through a posterior spinal defect
into into an expanded CSF filled dural sheath
(posterior meningocele).
The terminal syrinx component communicates
with the central canal of the spinal cord and the
meningocele component communicates with
the subarachnoid space.
The terminal syrinx and meningocele
components do not usually communicate with
each other.
53. REFERENCES
1. Acharya UV, Pendharkar H, Varma DR, Pruthi N, Varadarajan
S. Spinal dysraphism illustrated; Embroyology revisited. The
Indian journal of radiology & imaging. 2017 Oct;27(4):417.
2. Kumar J, Afsal M, Garg A. Imaging spectrum of spinal
dysraphism on magnetic resonance: A pictorial review. World
journal of radiology. 2017 Apr 28;9(4):178.
3. Rufener SL, Ibrahim M, Raybaud CA, Parmar HA. Congenital
spine and spinal cord malformations—pictorial review.
American Journal of Roentgenology. 2010
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