Caudal Regression Syndrome

MRI Sagittal T2w images of lumbo sacral spine shows:
Hypoplastic S1 and S2 with failure of formation of S3 and onwards. 

Cord ending at a higher level at D12-L1 with 'wedge' shaped termination.

No cord tethering.

No terminal cord cyst or syrinx. 

Imaging diagnosis : Caudal Regression, Group I. 

Synonyms: CRS, sacral agenesis, lumbosacral dysgenesis
Definition: Constellation of caudal developmental growth abnormalities with associated regional soft tissue anomalies of Spine.
Imaging wise best diagnostic clue: Lumbosacral dysgenesis with abnormal distal spinal cord.
Affects Lumbosacral spine.
Severity of diminution of caudal spine varies with case, ranging from absent coccyx to lumbosacral agenesis.
With an associated
Unilateral partial or total dysgenesis with oblique lumbosacral joint.
Bilateral total lumbosacral dysgenesis; vertebral column terminates in thoracic spine.
+/- Caudal vertebral bodies often fused.
+/- Severe canal narrowing rostral to last intact vertebra.
+/- Osseous vertebral excrescences, fibrous bands connecting bifid spinous processes, or severe distal dural tube stenosis.

Staging, Grading or Classification Criteria: 
Group 1:
More severe caudal dysgenesis with high-lying, ‘’club or wedge shaped ‘’ terminating cord (decreased number of anterior horn cells of cord, Distal cord hypoplasia with wedging seen in all patients with partial or complete dysgenesis and termination of spinal cord above Ll, Termination of the conus above Ll highly correlated with sacral malformations ending at Sl or above) so this group is associated with severe sacral osseous anomalies.  +/- dilated central canal, conus CSF cyst.
Group 2:
Less severe dysgenesis with low-lying, tapered, distal cord tethered by tight filum.
 (Conus termination below Ll highly correlated with sacral malformations ending at S2 or below) so this group is associated with milder sacral dysgenesis with tethered cord +/-  Lipoma, lipomyelomeningocele, or terminal myelocystocele.

Imaging wise DDs:  
Tethered cord:  Low-lying spinal cord +/- thickened or fatty filum, no caudal dysgenesis.
Closed spinal dysraphism:  Dorsal dysraphism without severe vertebral column agenesis.
Occult intrasacral meningocele : Sacrum thinned and remodelled, sometimes imitating caudal regression.

Etiology: 
Normal caudal spine development  includes canalization and retrogressive differentiation.
Anorectal and genitourinary structures form contemporaneously in close anatomic proximity.
Insult prior to fourth gestational week  result in caudal cell mass developmental abnormalities.
Signaling defects by retinoic acid and sonic hedgehog during blastogenesis and gastrulation > Abnormal neural tube, notochord development > impaired migration of neurons and mesodermal
Cells.
Hyperglycemia, infectious, toxic, or ischemic insult postulated to impair spinal cord, vertebral formation.

Genetics: 
Most cases sporadic.
Inherited in the HLBX9homeobox gene (chromosome 7) , HLBX9also expressed in pancreas  so possible association between diabetes hyperglycemia and caudal regression.
Epidemiology:
1/7,500 births (milder forms> severe forms)
15-20% are infants of diabetic mothersi 1% of offspring from diabetic mothers affected.

Associated abnormalities  and anomalies: 
Association with VACTERL(10%), omphalocele, exstrophy bladder, imperforate anus, spinal anomaluies (10%), and Currarino triad syndromic complexes
Common associated abnormalities  Tethered cord (100% of CRS patients with conus terminating
below L1), Thickened filum (65%) +/- dermoid or lipoma.
Other spinal anomalies: Vertebral anomalies (22%), diastematomyelia, terminal hydromyelia (10%), myelomeningocele (35-50%), lipomyelomeningocele (10-20%), terminal myelocystocele (15%), Anterior sacral meningocele.
Cardiac anomalies: Congential cardiac defects (24%), pulmonary hypoplasia.
Genitourinary abnormalities (24%), Renal agenesis/ectopia, hydronephrosis, Mullerian duct malformations, urinary bladder malformation
Anorectal anomalies (particularly anal atresia), Higher the level of anal atresia  >  more severe
lumbosacral dysgenesis, genitourinary anomalies.
Orthopaedic abnormalities: Extreme cases with lower extremity fusion (sirenomelia).

Reference: Diagnostic imaging Spine / Jeffrey S. Ross MD, Michael Brant-Zawadzki, MD, FACR, Kevin R.Moore, MD, Julia Crim, MD, Mark Z. Chen, MD, Gregory L. Katzman, MD,