A 24-year-old woman at 18 weeks has a raised maternal serum alpha-fetoprotein. Targeted ultrasound shows concave scalloping of the frontal bones and a cerebellum curved around the brainstem with an obliterated cisterna magna. What is the most likely diagnosis in the fetus?

Open spina bifida with Chiari II malformation

Dandy-Walker malformation of the posterior fossa

Occipital encephalocele with microcephaly

Anencephaly with exposed brain tissue

An ultrasound at 12 weeks in a primigravida from Bihar shows absence of the cranial vault above the orbits, with exposed brain tissue. Failure of which embryonic event explains this?

Closure of the cranial neuropore

Closure of the caudal neuropore

Embryology: urogenital and neural tube

8 NEET-PG practice questions on Embryology: urogenital and neural tube, part of Anatomy. The first 8 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Easy
A 35-year-old man has a CT for ureteric colic. It incidentally shows both kidneys lying low, with their lower poles joined by a band of renal tissue in front of the aorta at the level of L3. Which structure stopped the ascent of these kidneys?
1. ASuperior mesenteric artery
2. BCoeliac trunk
3. CInferior mesenteric artery
4. DCommon iliac arteries
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Answer: C · Inferior mesenteric artery
This is a horseshoe kidney, the commonest renal fusion anomaly. The metanephric kidneys normally ascend from the pelvis to the lumbar region, but when their lower poles fuse the isthmus is caught under the root of the inferior mesenteric artery, so the kidneys stay low. The ureters pass in front of the isthmus, which predisposes to obstruction, stones and infection. Horseshoe kidney is common in Turner syndrome and trisomy 18.
- A: The superior mesenteric artery arises higher, at L1, above where the isthmus is held.
- B: The coeliac trunk arises at T12, far above the arrested kidneys.
- D: The common iliac arteries lie below the isthmus, not across its path.
Question 2 · Hard
A 17-year-old girl has never menstruated. She has normal breast development and normal pubic and axillary hair. The vagina is a 3-cm blind pouch, and ultrasound shows no uterus but two normal ovaries. Consider these statements about her likely condition: 1. Her karyotype is expected to be 46,XX. 2. Ovarian hormone production is normal. 3. Renal anomalies are a recognised association. 4. Serum testosterone is in the male range. Which statements are correct?
1. A1, 2 and 3 only
2. B1 and 2 only
3. C1 and 3 only
4. D1, 3 and 4 only
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Answer: A · 1, 2 and 3 only
Statements 1, 2 and 3 are correct. Absence of the uterus and upper vagina with normal ovaries and normal secondary sexual characteristics is Mayer-Rokitansky-Kuster-Hauser syndrome, from failure of the paramesonephric ducts in a 46,XX woman. The ovaries come from the gonadal ridge, not the Mullerian ducts, so oestrogen production and ovulation are normal. Renal agenesis or ectopia and skeletal anomalies are associated, so the kidneys are imaged. A male-range testosterone with scanty pubic hair would instead suggest complete androgen insensitivity.
- B: Leaves out the renal association, which is why renal imaging is part of the work-up.
- C: Leaves out statement 2: the ovaries are normal and produce oestrogen.
- D: Includes statement 4, which fits androgen insensitivity, and leaves out normal ovarian function.
Question 3 · Medium
A 24-year-old woman at 18 weeks has a raised maternal serum alpha-fetoprotein. Targeted ultrasound shows concave scalloping of the frontal bones and a cerebellum curved around the brainstem with an obliterated cisterna magna. What is the most likely diagnosis in the fetus?
1. ADandy-Walker malformation of the posterior fossa
2. BOccipital encephalocele with microcephaly
3. COpen spina bifida with Chiari II malformation
4. DAnencephaly with exposed brain tissue
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Answer: C · Open spina bifida with Chiari II malformation
The 'lemon sign' (frontal scalloping) and 'banana sign' (cerebellum wrapped around the brainstem) are cranial clues to an open spinal neural tube defect. Leakage of CSF through the open spinal lesion lowers intracranial pressure, and the hindbrain is pulled down into the foramen magnum (Chiari II malformation). Raised maternal serum AFP fits an open defect. The spine is then scanned to find the level of the myelomeningocele, which predicts motor outcome.
- A: Dandy-Walker shows an enlarged posterior fossa with a cyst, the opposite of an obliterated cisterna magna.
- B: An encephalocele is a sac of brain through a skull defect, seen directly rather than inferred from these signs.
- D: Anencephaly is obvious from absent skull vault and would be seen without these signs.
Question 4 · Easy
An ultrasound at 12 weeks in a primigravida from Bihar shows absence of the cranial vault above the orbits, with exposed brain tissue. Failure of which embryonic event explains this?
1. AClosure of the cranial neuropore
2. BClosure of the caudal neuropore
3. CFusion of the vertebral arches
4. DFormation of the notochord
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Answer: A · Closure of the cranial neuropore
This is anencephaly (acrania with exencephaly), an open neural tube defect. The neural tube closes in the fourth week, with the cranial (anterior) neuropore closing around day 25 and the caudal neuropore a couple of days later. Failure of cranial closure leaves the forebrain exposed and it degenerates, and the skull vault does not form. The condition is lethal, and periconceptional folic acid reduces the risk in later pregnancies.
- B: Failure of caudal neuropore closure causes open spina bifida in the lumbosacral region.
- C: Failure of vertebral arch fusion gives spina bifida, not absence of the skull vault.
- D: The notochord induces the neural plate; its failure does not cause this isolated defect.
Question 5 · Medium
A 15-year-old girl is brought to the endocrine OPD for short stature and absent periods. She has a webbed neck, a broad chest with widely spaced nipples and wide carrying angles. Renal ultrasound shows fusion of the lower poles of both kidneys. What is her most likely karyotype?
1. A46,XY
2. B47,XXX
3. C47,XXY
4. D45,X
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Answer: D · 45,X
Short stature, primary amenorrhoea, a webbed neck, a shield chest and cubitus valgus are features of Turner syndrome, most often 45,X. Renal anomalies occur in about a third of these girls, and a horseshoe kidney is the most typical. Streak ovaries cause hypergonadotropic hypogonadism, and coarctation of the aorta and bicuspid aortic valve must be looked for. Growth hormone and timely oestrogen replacement are the mainstays of treatment.
- A: 46,XY in a phenotypic girl suggests androgen insensitivity or gonadal dysgenesis, without Turner stigmata.
- B: 47,XXX women are usually tall with normal ovarian function.
- C: 47,XXY is Klinefelter syndrome, a tall male phenotype.
Question 6 · Medium
A 7-year-old girl has new daytime wetting and a slight limp. There is a tuft of hair over the lower lumbar spine, and X-ray shows unfused laminae of L5. MRI shows the conus medullaris ending at L4 with a thick filum terminale. What is the most likely diagnosis?
1. ALumbar meningocele with intact skin
2. BCervical syringomyelia with cord expansion
3. CSpina bifida occulta with tethered cord
4. DSacral agenesis (caudal regression)
Answer and explanation in LearnFree account
Question 7 · Medium
A 27-year-old woman in a fertility clinic has had two losses in the second trimester. 3D ultrasound shows two endometrial cavities and a deep notch in the external outline of the uterine fundus, with a single cervix. Which developmental error explains this anomaly?
1. AFailure of resorption of the uterovaginal septum
2. BComplete failure of fusion of the paramesonephric ducts
3. CIncomplete fusion of the paramesonephric ducts
4. DFailure of one paramesonephric duct to develop
Answer and explanation in LearnFree account
Question 8 · Hard
A baby is born with a lumbosacral myelomeningocele to a 26-year-old woman with juvenile myoclonic epilepsy who was seizure-free on a single anticonvulsant through pregnancy. She did not take folic acid. Which drug was she most likely taking?
1. ALevetiracetam
2. BLamotrigine
3. CSodium valproate
4. DPhenytoin
Answer and explanation in LearnFree account

Embryology: urogenital and neural tube

A 35-year-old man has a CT for ureteric colic. It incidentally shows both kidneys lying low, with their lower poles joined by a band of renal tissue in front of the aorta at the level of L3. Which structure stopped the ascent of these kidneys?

A 24-year-old woman at 18 weeks has a raised maternal serum alpha-fetoprotein. Targeted ultrasound shows concave scalloping of the frontal bones and a cerebellum curved around the brainstem with an obliterated cisterna magna. What is the most likely diagnosis in the fetus?

An ultrasound at 12 weeks in a primigravida from Bihar shows absence of the cranial vault above the orbits, with exposed brain tissue. Failure of which embryonic event explains this?

A 15-year-old girl is brought to the endocrine OPD for short stature and absent periods. She has a webbed neck, a broad chest with widely spaced nipples and wide carrying angles. Renal ultrasound shows fusion of the lower poles of both kidneys. What is her most likely karyotype?

A 7-year-old girl has new daytime wetting and a slight limp. There is a tuft of hair over the lower lumbar spine, and X-ray shows unfused laminae of L5. MRI shows the conus medullaris ending at L4 with a thick filum terminale. What is the most likely diagnosis?

A 27-year-old woman in a fertility clinic has had two losses in the second trimester. 3D ultrasound shows two endometrial cavities and a deep notch in the external outline of the uterine fundus, with a single cervix. Which developmental error explains this anomaly?

A baby is born with a lumbosacral myelomeningocele to a 26-year-old woman with juvenile myoclonic epilepsy who was seizure-free on a single anticonvulsant through pregnancy. She did not take folic acid. Which drug was she most likely taking?