Correlation between ultrasound diagnosis and autopsy findings of fetal malformations: about 31 cases

Objective:

To describe the correlation between prenatal ultrasound findings and autopsy observations in fetuses with developmental anomalies diagnosed at a gestational age between 13 and 33 weeks.

Methods:

This is a retrospective study over a 2-year period from 2013 to 2015. 31 pregnancies terminated after prenatal identification of severe fetal malformations were evaluated by post mortem examination. Inclusion criteria: women admitted in our department in whose prenatal ultrasound fetal abnormalities were reported.

Results:

Fetal autopsy confirmed the ultrasound findings in all cases (100%). In 10 (32. 2%) cases there was complete concordance between prenatal and autopsy findings, while in 21 cases the fetal autopsy findings showed more abnormalities. There were 6 cases with isolated malformations, 25 cases with multiple malformations. Among the 25 polymalformations: 18 (72%) were detected prenatally and 7 (28%) were detected after fetal autopsy. The additional malformations detected on autopsy included 2 major and 5 minor malformations. Additional findings helped in redefining the diagnosis and the risk of recurrence in 20% of cases.

Discussion:

In our study, we compared prenatal ultrasound, as diagnostic tool to detect fetal malformations in the pregnancy, and autopsy to evaluate US diagnostic accuracy. Even if some defects could be observed now in very early pregnancy, the main method to detect fetal structural anomalies is the second trimester US examination, performed at about 22 gestational weeks.

Previously, several studies stressed the correlation between US and pathology, often regarding fetal autopsy as the 'gold standard' and evaluating the 'specificity' and the 'sensitivity' of US towards autopsy. The 'sensitivity', in particular, does not seem to be elevated and it would not be over 40%. Those studies are very different in their inclusion criteria. Most of them included fetuses from all gestational weeks, spontaneous abortions and neonatal deaths.

The conclusions of the study of Kanseen et al. showed discrepancies between US and autopsy findings in about 40% of cases, and that confirms the importance of pathological examination after every termination of pregnancy.

Most of these studies were retrospective in nature, as ours. In 2007 Akgun et al. published a prospective study concluding that evaluation of fetal autopsies following termination of pregnancy enables the diagnosis of pathologies undetected by prenatal US.

In the 2008 study by Antonsson et al., US and autopsy were examined on the same methodological basis, in order to analyze the potential and limitation not only of US, but also of autopsy to reach a correct diagnosis. In that study it was pointed out that, in some cases, autopsy could have significant limitation, mainly concerning the diagnosis of CNS malformations. In fact, other studies demonstrate that postmortem magnetic resonance imaging (MRI) has a useful role in providing structural informations of the central nervous system in fetuses and stillbirth neonates. We performed fetal MRI before the termination of pregnancy only in 10 cases because in all the others the patients had already decided to terminate pregnancy or the diagnosis was clear at US. It is understandable that an US examination performed in a tertiary center, with machines of better quality, by experienced examiners and so with more regard to congenital anomalies, turns out to be more accurate than an examination performed in a not specialized structure.

In a few cases at autopsy the pathologist found out additional anomalies not really detectable at US. Actually, renal cystic disease may be difficult to define on a scan because of a lack of amniotic fluid; moreover, the differentiation between infantile polycystic kidney disease and the cystic renal dysplasia may require histological examination.

Moreover US evaluation of the spine can be limited by oligohydramnios, maternal obesity and fetal position. Shadowing from the bony structure can also preclude a complete evaluation of the spinal cord and arachnoid sac. Also demonstration of corpus callosum on US is difficult. This leads to miss some diagnosis and because of those limitations a lot of studies have compared MRI and US for diagnosis of CNS anomalies, pointing out that MRI can be a good supplement to US in complicated pregnancies.

In 28% of cases, autopsy provided additional information about clinically relevant anomalies not previously detected at US.

So, it has been evidently shown that both US and autopsy may have some important limitations in diagnosing fetal abnormalities and that the two exams are complementary. This means that a diagnosis made in a tertiary center is related to a higher detection rate of fetal malformations, mainly concerning functional defects, and to a smaller number of false negatives. This is very important because a correct diagnosis, in addition to a multidisciplinary counseling in a specialized center, affects the couple's decision to terminate pregnancy and maybe it could reduce the number of termination of pregnancy in the future.

Conclusion:

Evaluation of fetal autopsies following TOP enables diagnosis of pathologies undetected by prenatal ultrasound alone, leading to better preconceptional counseling for subsequent pregnancies.