The position of the stomach in patients with left sided BH was correlated with prognosis[9], and imaging physicians should assessed whether the stomach enters the chest cavity on preoperative imaging.In this study, one-third of patients with left sided BH were determined intrathoracic stomach by preoperative imaging,much lower than that in surgery found.The proportion of intrathoracic stomachs detected by imaging was also smaller than the proportion reported in other studies[15, 17].There have been only a few studies of late onset left sided BH, and most of them were in the form of case reports.This study calculated the the ratio of intrathoracic stomachs in late onset BHs, and the proportion identified by imaging was still 34.7%, indicated that nearly one third of the patients with delayed manifestation may still have a serious condition.
The proportion of left sided BH patients with intrathoracic stomach detected via preoperative imaging was lower than that reported in the existing literature, which was more than 50%[15, 17]. There may be several factors that contributed to the increased proportion of intrathoracic stomach reported in other studies.Firstly, rather than applied a single method for diagnosed BH, this study used multiple postnatal imaging techniques.Secondly, previous studies had measured the percentage of intrathoracic stomach in patients with CDH. As mentioned above, there were 25–30% of CDH that did not belong to BH[2], and if we had included children with hiatal hernias in our study, the proportion of intrathoracic stomach might have been higher. Furthermore, extensive eventration of a hemidiaphragm may also increase the proportion of intrathoracic stomachs detected in patients with BH, but it is extremely difficult to differentiate this abnormality from CDH on prenatal imaging[18].Of course, perinatal death may also result in a lower rate of herniation of the stomach into the chest cavity after birth than in the foetal period.
In this study, the proportion of the intrathoracic stomach that was found on imaging was smaller than that was found during surgery. The possible reason for this is that the herniation of abdominal organs in patients with diaphragmatic hernia are related to abdominal pressure.In patients with a diaphragmatic hernia, coughing, burping and flying can all increase the likelihood of abdominal hernias into the chest cavity[19, 20].So the position of the stomach that is detected during the procedure is not constant. The surgical procedure disrupts normal physiological conditions and may induce abnormal chest and abdominal pressures.For example, tracheal intubation and mechanical ventilation during surgery can lead to excessive inflation of the gastrointestinal tract and an increase in abdominal pressure.In addition, the thoracic surgical approach may cause partial compression of the lungs, increasing the possibility of gastrointestinal hernia entering the chest cavity.
Among the late onset patients in this study,nearly a third had intrathoracic stomach as determined by preoperative imaging,which was rarely reported.Another one study reported that six out of 17 patients (35.3%) with delayed left-sided CDH had an intrathoracic stomach[21].There were several reasons that could explain the delayed appearance of clinical manifestations in BH.First of all, if the diaphragmatic defect was small, some solid organs may prevented the gastrointestinal tract from herniating into the chest. Some studies had suggested that a small diaphragm defect may be contributed to the low ratio of the intrathoracic stomach. Secondly, the respiratory movement caused pressure change in the chest, with the abdominal organs being constantly pulled and pushed by the pressure changes. Finally, there had been reports of defects or absence of gastrophrenic and gastrosplenic ligaments in patients with CDH[22],and in these patients, the stomach might herniated into the chest. Nevertheless, after the gastric hernia entered the chest cavity, the stomach cannot easily returned to the abdominal cavity due to the small diaphragmatic defect and stomach distension. Some patients may even had acute obstruction or perforation due to gastric torsion[22, 23].
In summary, this study suggested one-third of left-sided BHs may develop intrathoracic stomachs as determined by preoperative imaging.This also suggested that severe Bochdalek hernia was lower than previously reported in neonatal BHs.But attentions should still be paid to late onset BHs, because of one third of children still had intrathoracic stomachs, which were prone to serious complications.
This is a single centre study and this study was conducted in a specialised children's hospital,thus adult patients with late onset BHs were not included in this study population.Therefore,large samples are needed to evaluate the image features of BHs and the ratio of intrathoracic stomachs, in order to guide the treatment and predict prognostication.