Mechanisms of intradural gas on post mortem magnetic resonance imaging

• Intradural extramedullary gas in the spinal canal on PMMR has not been described.
• We identified intradural gas in foetuses with open neural tube defects.
• This finding may help in correctly interpreting perinatal PMMR in the future.

ObjectivesThe significance of observing intracranial, intrathoracic and intraabdominal gas on post mortem MRI (PMMR) has been attributed to iatrogenic introduction, fetocide, or body decomposition. Intradural extramedullary gas tracking along the spinal cord on foetal PMMR has not been described, and we hypothesise that it may only occur in suspected neural tube defects (NTD), as open spinal dysraphisms may allow free passage of air into the spinal canal during delivery.MethodsWe reviewed 76 foetal PMMRs performed in our institution. We categorised cases into those who had a NTD confirmed at perinatal autopsy, or had been terminated or stillborn of other causes. We documented the presence of intradural gas and gas elsewhere in the body.ResultsWe compared the PMMR findings in 13 foetuses who had NTD confirmed at autopsy (median gestation 20 weeks) against 63 age-matched normal controls (median gestation 20 weeks). All four cases of intradural gas occurred in foetuses with an open NTD (4/13; 31%), with none seen in normal controls (0/63; p<0.001).ConclusionIntradural extramedullary gas on foetal PMMR is associated with open neural tube defects.