IPLab:Lab 13:Myelomeningocele

Clinical Summary

This male fetus of a 21-year-old Rh-positive mother (Gravida 2 Para 1011) was the product of an induced delivery at 21 weeks gestation. At 19 weeks gestation, routine prenatal examination had revealed a maternal serum alpha-fetoprotein (AFP) level that was 4.2 times the mean for a mother at this point in gestation. A targeted ultrasound was ordered--which revealed a lumbosacral neural tube defect--and an amniocentesis was performed. Amniotic fluid showed an AFP level that was 5.3 times the calculated median value and cytogenetic analysis demonstrated a normal male (46XY) chromosome pattern. The parents requested termination of the pregnancy and a 465-gram male nondysmorphic stillborn fetus was delivered vaginally.

Autopsy Findings

There was a myelomeningocele in the lumbar region that measured 1.6 cm in width and 3.7 cm in length.

Images

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  This is a gross photograph of the fetus at autopsy. Note the defect in the lower lumbar region of the spinal column (arrow). The myelomeningocele can be seen protruding from this defect.

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  This gross photograph shows consecutive lumbar vertebra from this case. Note the defect (arrows) in the two vertebral bodies on the right. This defect was caused by failure of the vertebral column to properly close.

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  This is a closer view of the previous gross photograph showing a normal lumbar vertebra from this case on the left. Once again, note the defect (arrow) in the vertebral body on the right due to failure of the vertebral column to close properly.

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  This is a low-power photomicrograph of one of the vertebral bodies from this case. In this section there are defects (arrows) in the vertebral body but the skin can be seen over the open vertebral canal.

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  This is a higher-power photomicrograph of one of the vertebral bodies from this case. The defect (arrows) in the vertebral body is seen more clearly. The spinal cord is disrupted and there are areas of hemorrhage in this region.

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  This is a high-power photomicrograph of the spinal cord (arrow) immediately beneath the area of hemorrhage.

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  This high-power photomicrograph of the spinal cord within the vertebral column shows the hemorrhage (arrows) in this region.

Study Questions

• What are the various types of neural tube defects?

Neural tube defects (NTD) are abnormalities of both neural tissue and overlying bone and/or soft tissues which result in failure to close of a portion of the neural tube or reopening of a region that had previously been closed. The most common forms of NTD in newborns involve the caudal portions of the spinal cord.

NTDs may include:

• Anencephaly - malformation of the anterior neural tube leading to failure of the brain and calvarium to develop
• Encephalocele - diverticulum of malformed brain tissue extending through a hole in the cranium.
• Spinal dysraphism or spina bifida - asymptomatic bony defect (spina bifida occulta) or a severe malformation with a flattened, disorganized segment of spinal cord, associated with an overlying meningeal out-pouching.
• Meningocele - defect in the spinal column with meningeal tissue extending through it.
• Myelomeningocele - defect in the spinal column with meningeal and spinal cord tissue extending through it.

• What is the etiology of neural tube defects?

The etiology of NTDs is generally unknown, though most NTDs appear to be due to multifactorial inheritance and environmental factors.

The frequency of NTDs varies widely among ethnic groups and there is a recurrence rate for NTDs in subsequent pregnancies of approximately 4 to 5%.

Recent evidence has shown that folate deficiency during the first few weeks of gestation increases the risk of NTDs. Other risk factors include diabetes mellitus, hyperthermia, alcohol ingestion and exposure to other toxic substances.

• What kinds of clinical problems can be seen in patients with myelomeningoceles?

Clinical problems can result from damage to the spinal cord due to the myelomeningocele or due to secondary infection.

Clinical deficits usually occur in motor and sensory function in the lower extremities as well as disturbances of bowel and bladder control.