Fetal and neonatal outcomes of posterior fossa anomalies: a retrospective cohort study

The primary aim of this study was to estimate the incidence of posterior fossa anomalies (PFA) and assess the associated outcomes in King Abdulaziz Medical City (KAMC), Riyadh. All fetuses diagnosed by prenatal ultrasound with PFA from 2017 to 2021 in KAMC were analyzed retrospectively. PFA included Dandy–Walker malformation (DWM), mega cisterna magna (MCM), Blake's pouch cyst (BPC), and isolated vermian hypoplasia (VH). The 65 cases of PFA were 41.5% DWM, 46.2% MCM, 10.8% VH, and 1.5% BPC. The annual incidence rates were 2.48, 2.64, 4.41, 8.75, and 1.71 per 1000 anatomy scans for 2017, 2018, 2019, 2020, and 2021, respectively. Infants with DWM appeared to have a higher proportion of associated central nervous system (CNS) abnormalities (70.4% vs. 39.5%; p-value = 0.014) and seizures than others (45% vs. 17.9%; p-value = 0.041). Ten patients with abnormal genetic testing showed a single gene mutation causing CNS abnormalities, including a pathogenic variant in MPL, C5orf42, ISPD, PDHA1, PNPLA8, JAM3, COL18A1, and a variant of uncertain significance in the PNPLA8 gene. Our result showed that the most common PFA is DWM and MCM. The autosomal recessive pathogenic mutation is the major cause of genetic disease in Saudi patients diagnosed with PFA.

This study aims to estimate the incidence and identify the different types of posterior fossa abnormalities in the King Abdulaziz Medical City (KAMC) population and assess the outcomes associated with different types of PFA, such as neurologic development, from 2017 to 2021.
Over the 5 years, the cases of PFA were distributed as follows: 41.5% DWM, 46.2% MCM, 10.8% VH, and 1.5% BPC.The mean and standard deviation (SD) of maternal age was 31.6 ± 6.5 years.Approximately 14% of the mothers were primigravid.The prevalence of miscarriage was 38.5% among the mothers in this study.Approximately one-third of mothers in the study reported they were married consanguineously.Further, associated CNS abnormalities and extra CNS abnormalities were found in 52.3% and 41.5%, respectively, of the cases.A full description of the maternal and infant characteristics is included in Table 1.
Table 2 includes the maternal and infant characteristics of the two major posterior fossa anomalies diagnosed in the KAMC.Infants with DWM appear to have a higher proportion of associated CNS abnormalities than those without DWM (70.4% vs. 39.5%;p-value = 0.014).On the other hand, infants with MCM appear to have a significantly lower proportion of associated CNS abnormalities than those without MCM (36.7% vs. 65.7%;p-value = 0.019).Further, infants with DWM appear to have a higher proportion of dysmorphology than those without DWM (60.9% vs. 30%; p-value = 0.025).Further, compared to those without DWM, those with DWM had an abnormal neurological exam (70% vs. 37.9%; p-value = 0.027) and abnormal head and neck examination (63.2% vs. 29.2%;p-value = 0.026).Also, Infants with DWM appear to have a higher proportion of seizures than those without DWM (45% vs. 17.9%;p-value = 0.041).Finally, those with DWM were more likely to undergo neurosurgical intervention than those without DWM (30% vs. 6.9%;p-value = 0.049).On the other hand, those with MCM were not significantly different in the distribution of several maternal and infant characteristics from those without MCM (Table 2).
A diagnosis of Dandy-Walker malformation was found in 27 pregnancies in total; CNS abnormalities were diagnosed in 20 cases, including absent cavum septum pellucidum in six fetuses and bilateral dilated lateral ventricles with absent cavum septum pellucidum in four, two fetuses were diagnosed with agenesis of the corpus callosum and eight with dilated lateral ventricles.Regarding the extra-CNS, a total of 10 pregnancies were identified, seven with cardiac anomalies and three with renal anomalies.Eleven fetuses diagnosed with MCM had associated CNS abnormalities: four with absent cavum septum pellucidum, four dilated lateral ventricles, two with agenesis of corpus callosum, and one with small cerebellum.Extra-CNS abnormalities in MCM were found in 11 cases, four with renal anomalies, including absent single kidney, polycystic kidney, and dilated renal pelvis.Three of MCM had hydrops fetalis.One was diagnosed with Down syndrome, the second one ended with stillbirth, and there was missing data for the third case.Cardiac anomalies were identified in three pregnancies with MCM and echogenic bowel in one case.VH was diagnosed in seven cases; three of them had associated CNS abnormalities, two with abnormal absent cavum septum pellucidum, one with dilated posterior fossa, and one diagnosed postnatally with Joubert syndrome.Only one of the VH cases had extra-CNS abnormalities,   3) shows the details of this dysmorphology and the associated PFA.
Fetal karyotype was performed in 21 cases, providing five abnormal karyotypes, two fetuses with MCM associated with CNS anomalies and three fetuses with DWM associated with CNS and non-CNS abnormalities.The abnormal karyotyping results were 4 trisomy 18 and 1 trisomy 13.
Genetic testing was done for 17 infants; 12 had abnormal results.Among the 12 patients, two infants had abnormal karyotypes, one had trisomy 18, and the other had a heterozygous likely pathogenic deletion within the cytogenic band 2q.23.1(147940954_148024399).The rest have a single gene mutation causing CNS abnormalities; four patients have pathogenic variants in different genes known to have CNS abnormalities, one patient with a pathogenic variant in the MPL gene, two affected infants with different variants in C5orf42 gene, the fourth patient has a pathogenic variant in ISPD gene (Table 4).
We also identified four patients with likely pathogenic variants in the following genes PDHA1, PNPLA8, JAM3and in COL18A1 genes causing CNS manifestations.Also, one patient has a different variant of uncertain significance in the PNPLA8 gene that suggests its rule for pathogenicity.Finally, we found two variants in two different genes in an infant with ventriculomegaly osteopetrosis (Table 4).

Discussion
Our study's findings showed a single-tertiary center experience and indicated that DWM and MCM were the most common PFA, consistent with other research 3 .Incidence rates per 1000 anatomy scans were 2.48, 2.64, 4.41, 8.75, and 1.71 for 2017, 2018, 2019, 2020, and 2021, respectively.DWM is a rare disease with an estimated incidence of 1 per 30,000 births 10,11 13,14 .Our findings showed a slightly higher percentage, with 78.6% of DWM cases diagnosed postnatally as developmental delay; Hydrocephaly was developed in only six cases.However, hydrocephalus was reported as the most frequent CNS complication in DWM, and Venkatesan et al. results showed there is a high risk of requiring a ventriculoperitoneal shunt and developing epilepsy during early childhood [15][16][17] .In addition, the results of a previous systematic review demonstrate an increased risk of abnormal neurodevelopmental outcomes in children with a prenatal diagnosis of isolated DWM 18 .
In general, the reported neurodevelopmental outcome of isolated MCM is favorable 18 , similar to our study of seven cases of isolated MCM with a normal neurodevelopmental outcome.However, concurrent CNS www.nature.com/scientificreports/abnormalities were related to a worse prognosis in children with MCM 8 ; in our study, all cases of MCM associated with CNS abnormalities were diagnosed later as a developmental delay, except one patient was diagnosed with cytomegalovirus (CMV) infection.The precise diagnosis of isolated BPC is not always simple and is not confirmed prenatally in some cases 3,19 .Our result showed one case of BPC was diagnosed prenatally but was not confirmed postnatally as the diagnosis was DWM with no ventriculomegaly by postnatal MRI.The existence of extra CNS anomalies was correlated with a worse prognosis compared to the absence of such abnormalities 5 .CNS-associated abnormalities were 52% in cases of DWM and MCM, which is consistent with a recent study's finding that CNS was the most frequent ultrasound abnormality 20 .The most frequently observed extra CNS anomalies were renal and congenital heart disease in 27.7% and 23.1% of all PFA cases, respectively, which is similar to the previous study's result 20 .Our result is consistent with the previous report, which showed the most frequent extra CNS anomalies were infantile polycystic kidneys in DWM infants 21 .In addition, eight cases with congenital heart disease were found to have developmental delays.According to Seker et al., cardiac anomalies play a crucial impact in infant prognosis 22 .There have been reports of concomitant dysmorphology similar to our study's findings, including deformities of the face and a cleft palate and lip 20,23,24 .
Genetic and chromosomal abnormalities are important factors in DMW etiology 25 .Although a normal karyotype can coexist with DWM, the 3rd, 9th, 13th, and 18th chromosomes are most frequently linked to concurrent chromosomal abnormalities 26 .In our study, genetic testing was performed on 17 patients, of which 12 had abnormal results.Total (fetal and postnatal) karyotype was performed in 23 cases, of which six had abnormal results.We have found 12 infants with abnormal results, two with abnormal karyotypes, and the remaining ten with gene mutations.Among the patients with abnormal karyotypes, we found four cases with trisomy 18 and one with trisomy 13, known in previous studies to be associated with posterior fossa anomalies 25 .The other case has microdeletion in the cytogenetic band 2q23.1, which was not known to be associated with posterior fossa abnormalities 27 .From this study, we cannot conclude if the PFA are a coincidence or an expanding phenotype for this microdeletion.Further study is needed to clarify this association.The remaining ten infants have a single gene mutation, including the MPL gene, which causes rare inherited bone marrow failure syndrome, which was reported in one case report to be associated with hypoplastic cerebellar vermis with a communication between the fourth ventricle and the cisterna magna 28 .Two affected infants with different variants in the C5orf42 gene caused Joubert syndrome type 17, which was not specifically associated with posterior fossa anomalies.However, www.nature.com/scientificreports/Joubert syndrome was reported in some cases with PFA, including DWM 29 .The fourth patient has a pathogenic variant in the ISPD gene causing Muscular dystrophy-dystroglycanopathy, which is known to be associated with DWM 30 .We also identified four patients with likely pathogenic variants, including PDHA1 causing Pyruvate dehydrogenase E1-alpha deficiency, JAM3 causing hemorrhagic destruction of the brain, subependymal calcification, and congenital cataracts (HDBSCC) with the neonatal onset and COL18A1 gene causing Knobloch syndrome, type 1.All genes are known to be associated with CNS manifestations; however, none of them is reported to be associated with PFA [31][32][33] .In addition, two patients were found to have a PNPLA8 gene mutation, which causes mitochondrial myopathy with lactic acidosis, and it was not reported previously with PFA 34 .Finally, we have identified one infant with two variants in two different genes; one gene is MTMR2, causing Charcot-Marie-Tooth disease, type 4B1, and the other is aTCIRG1, causing osteopetrosis, autosomal recessive 1 35,36 .The latter has been reported in one case of severe autosomal recessive osteopetrosis associated with Dandy-Walker syndrome and agenesis of the corpus callosum 37 .Non-genetic contributor to PFA is infection 38 .According to certain reports, PFA may be related to CMV infection 39,40 .Intracranial calcification is the most frequent abnormality observed in infants with congenital CMV infection on neuroradiologic imaging, in addition to other intracranial abnormalities that include ventriculomegaly, white matter abnormalities, neuronal migration abnormalities, and extensive destructive encephalopathy 40 .We reported one case of congenital CMV in which prenatal ultrasound showed mega cisterna magna associated with right ventriculomegaly.
The consanguineous marriage rate is 51% in Saudi Arabia 41 .According to our findings, one-third of the parents of fetuses with PFA were consanguineous, and 61% of these fetuses have abnormal genetic testing.Our results show that half (7 out of 13) of the genetic testing is an autosomal recessive disease which is supported by a previous study that demonstrates autosomal recessive pathogenic mutation is the major cause of genetic disease in Saudi patients 42 .In addition, previous data showed a high proportion of DWM in consanguineous marriages, reaching 44% 21 .
To our knowledge, this is the only study of fetal posterior fossa anomalies in Saudi Arabia.Although it is limited because it is retrospective, with missing data and a small sample size, it provides information on posterior fossa anomalies in our population and the association of genetic disease in consanguineous marriage.MRI criteria for diagnosing DWM were classic since it is a retrospective study from 2017 to 2021, and this is one of the limitations.The criteria that most accurately characterize the modern DWM phenotype are an enlarged tegmentovermian angle, an obtuse fastigial recess, an unpaired caudal lobule (tail sign), inferior, predominant VH, and inferolateral displacement of the tela choroidea/choroid plexus 43 .

Conclusion
The most common PFA in the KAMC population is DWM and MCM.Developmental delay is more likely when there are associated CNS anomalies.The autosomal recessive pathogenic mutation is the major cause of genetic disease in Saudi patients diagnosed with PFA, and the possibility of identifying new phenotypic associations is high.Therefore, preconception and genetic counseling programs should be implemented for the consanguineous parents.

Methods
This was a retrospective, single-center cohort study conducted between January 2017 and December 2021 in King Abdulaziz Medical City (KAMC), Riyadh, Saudi Arabia.KAMC is one of the largest tertiary centers in the region, with 1973 beds.The Department of Obstetrics and Gynecology performs about 8000 deliveries each year, with mother and fetal outcomes similar to international standards 44 .Initially, cases were identified from the perinatal review meeting list held weekly to discuss the new fetal cases in the clinic.All fetuses diagnosed with PFA were included.The diagnosis was made according to transabdominal ultrasound mid-trimester examination images using the standard axial planes for screening exams, including trans ventricular, trans thalamic, and trans cerebellar planes 45 , which were reviewed and confirmed by a fetal-medicine consultant.A fetal MRI was ordered when diagnostics certainty was required.The MRI criteria for diagnosing DWM include lack of the lower part of the vermis, anterior rotation, upward displacement, and hypoplasia of the remaining vermis.The fastigium's

Figure 1 .
Figure 1.Frequency and Incidence* of Posterior Fossa Abnormalities in the KAMC-Riyadh, Saudi Arabia between 2017 and 2021.*Incidence was calculated as number of the posterior fossa abnormalities per total number of anatomy scans.DWM Dandy-Walker malformation, MCM mega cisterna magna, BPC Blake's pouch cyst, VH isolated vermian hypoplasia.

Table 1 .
12ternal VP shunts; however, our findings showed fewer patients needed VP shunts, 30%12.The majority of DWM cases in our study have been associated with CNS and extra CNS anomalies.DWM infants, therefore, have a high rate of seizure occurrence.Previous neurosurgical series indicate that the combination of DWM and hydrocephalus is associated with abnormal neurologic development in 40-70% of survivors 3 A common CNS finding in DWM cases is ventriculomegaly3, which might need a ventriculoperitoneal (VP) shunt in severe cases.A previous study found that 62.7% of DWM cases and infant characteristics of posterior fossa anomalies diagnosed in the KAMC-Riyadh, Saudi Arabia.DWM Dandy-Walker malformation, MCM mega cisterna magna, BPC Blake's pouch cyst, VH isolated vermian hypoplasia, CNS central nervous system, MRI magnetic resonance imaging, FGR fetal growth restriction, NICU neonatal intensive care unit, WES whole exome sequencing, WGS whole genome sequencing, CGH comparative genomic hybridization, NGT nasogastric tube, OGT orogastric tube, TPN total parenteral nutrition, GT gastrostomy tube.required

Table 2 .
Maternal and infant characteristics by the two major posterior fossa anomalies diagnosed in the KAMC-Riyadh, Saudi Arabia.DWM Dandy-Walker malformation, MCM mega cisterna magna, CS cesarean section, CNS central nervous system, NICU neonatal intensive care unit.