Low-field MRI sheds light on neonatal complications

October 1, 2007

Researchers from the U.K. have found that clinically silent subdural and extracranial hemorrhages in babies can be detected by low-field MR systems.

Researchers from the U.K. have found that clinically silent subdural and extracranial hemorrhages in babies can be detected by low-field MR systems.

Their analysis of 315 newborns at Sheffield's Royal Hallamshire Hospital revealed that many subdural bleeds are located in the posterior fossa and occur most often in instrumental deliveries. Extracranial hemorrhages were associated with vacuum delivery.

"Symptomatic neonates may have additional pathology to subdural bleeds because all the intracranial bleeds in this study were asymptomatic," said Dr. Lauren Wallis, a postdoctoral research associate at the hospital's academic radiology unit. "Isolated subdural hemorrhages resolve spontaneously, do not appear to rebleed, and if they occur in infants over four weeks of age, may be suggestive of nonaccidental injury rather than birth injury."

It is well known that using vacuum extractors in vaginal operative deliveries may cause neonatal complications, including extracranial bleeding. In a previous study by the Sheffield group, MR imaging of 111 asymptomatic neonates revealed nine infants with unilateral or bilateral subdural hemorrhage (Whitby E et al. Lancet 2004;12(363):2001-2002). These resolved spontaneously within four weeks and did not rebleed.

Wallis and her colleagues wanted to determine if the high number of asymptomatic subdural bleeds was reflected in an increased number of extracranial bleeds, and if the mode of delivery influenced the occurrence of intra- and extracranial bleeds. They performed MR examinations on term babies within 48 hours of delivery. Images were acquired using a permanent magnet system operating at 0.2T (7.2 MHz, InnerVision MRI, London), using 15 mc/m gradients and installed in a modular screened enclosure within a room on the neonatal intensive care unit.

T1-weighted axial and coronal and T2-weighted coronal images were obtained with an inplane resolution of 1-mm and 5-mm slice thickness. No sedation or anesthesia was used.

Obstetric details were recorded retrospectively from notes on the patient, including parity, onset of labor, mode of delivery, and indications for operative delivery. Details of the position and station of the fetal head, degree of caput and molding, presence of meconium, presence of cord around neck, need for pediatric resuscitation, and Apgar scores at one and five minutes were also recorded.

A neonatal radiologist who was unaware of the obstetric details interpreted the MR images and measured subdural hemorrhage maximum depth in the axial plane. Incidence of subgaleal hemorrhage, cephalohematoma, and other extracranial bleeds was also noted. Odds ratios were calculated for subdural bleeding and cephalohematoma for each mode of delivery, using the normal vaginal delivery group as the baseline.

Wallis presented the group's results at the joint annual ISMRM/ESMRMB congress held in Berlin in May. Of the 315 neonates, 21 (6.8%) had a subdural bleed. These were found in all delivery methods except cesarean sections, with the highest incidence following Ventouse delivery. The majority were located in the posterior fossa. All had resolved by four weeks of age, with no rebleeds to date. All were, and remained, clinically silent. A total of 3.17% of the babies had a subgaleal bleed, and 1.9% had a cephalohematoma.

The distribution of extracranial bleeds reflected the distribution of subdural bleeds with respect to the method of delivery, but these were not usually the same patients, Wallis said. In 36 cases, the delivery method was Ventouse only, and four of these patients had a subdural bleed, amounting to a risk of 11.1%. In 22 cases, the method of delivery was Ventouse to forceps, and six of these patients had a subdural bleed, amounting to a risk of 27.3%. In 20 cases, delivery method was forceps only, resulting in two subdural bleeds and a risk of 10%. In 183 cases, there was a normal vaginal delivery, leading to nine subdural bleeds and a risk of 4.9%.