The sac contents decide the diagnosis. Meninges only is meningocele. Meninges plus neural tissue is myelomeningocele.
Before you scroll: A newborn has a lumbosacral sac protruding from the back. The sac contains meninges but no neural tissue. Neurologic examination of the lower extremities is normal. Which diagnosis best explains this finding?
Meningocele is the middle bucket: there is a sac, but it contains only protective membranes and cerebrospinal fluid. The spinal cord stays in the canal, so the brain and nerve exam can be normal. Myelomeningocele adds spinal cord tissue to the sac and causes weakness below the defect. Occulta has no sac. Sac with protective membranes only + normal brain and nerve exam = meningocele.
Sac contents
What Is In the Sac?
The board answer follows the contents: no sac, meninges only, meninges plus cord, or open neural plate.
Spina bifida occulta
Closed posterior arch defect
SkinCovered
SacNone
Neural tissueNot herniated
SignalHair tuft, dimple, normal alpha-fetoprotein, often normal exam
Meningocele
Protective membranes only
Skin/sacProtruding protective-membrane sac
ContentsProtective membranes and cerebrospinal fluid, no cord
Neuro examOften normal
TrapA sac does not automatically mean myelomeningocele
Myelomeningocele
Meninges plus neural tissue
ContentsMeninges plus spinal cord or nerve roots
Neuro examDeficits below the lesion
ScreeningOften elevated alpha-fetoprotein and acetylcholinesterase
AssociationChiari II and hydrocephalus
Myeloschisis and anencephaly
Open neural tissue
MyeloschisisOpen flattened neural plate without a covered sac
AnencephalyFailure of cranial closure with absent calvarium/forebrain
ScreeningOpen defects elevate alpha-fetoprotein
TrapRostral defect is not a lumbosacral sac
Board trap: Do not call every lumbosacral sac myelomeningocele. Myelo means neural tissue is in the sac.
Defect switchboard
Read the Sac
Pick the physical finding. The readout names the defect and why.
Which defect matches this newborn finding?
Pick a clue.Ask: Is there a sac? If yes, what is inside it? If neural tissue is exposed, how open is it?
Board trap: Normal lower-extremity neurologic exam strongly supports meninges-only meningocele rather than myelomeningocele.
Two-gate discriminator
Decision Tree
First decide whether there is a sac. Then decide whether neural tissue is inside it.
1
Is there a protruding lumbosacral sac?
No sac, just closed skin findings like a dimple or hair tuft.
Yes, there is a sac or exposed tissue.
2
Does the sac contain spinal cord or nerve roots?
No. Protective membranes and cerebrospinal fluid only.
Yes. Neural tissue is in the sac or exposed.
3
Is the neural tissue contained in a sac or open as a flat exposed plate?
Contained in a sac with deficits below the lesion.
Open exposed neural plate without a clean sac.
Make it stick
Hooks and Images
Say the contents out loud: no sac, meninges only, meninges plus cord, open plate.
Spina bifida · tap to expand
Neural tube · tap to expand
Spina bifida · tap to expand
Board walkthrough
Prove It
One vignette at a time. Choices shuffle. The bank does not repeat until it is exhausted.
Vignette 1Never-repeat tracking ready
Exam tools: right-click or long-press to cross out a choice. Double-click or double-tap to highlight one. Tools switch off after you answer.
