The most generally accepted nomenclature of hiatus hernia includes four categories: Type I (sliding hernia) which accounts for approximately 95% of cases of hiatal hernia, Type II (paraesophageal hernia) which accounts for approximately 5% of cases of hiatal hernias, and Type III which is a combination of both Type I and II. Type IV, parahiatal hernia, is also gaining widespread acceptance in the literature. Parahiatal hernia (Type IV) is differentiated from the foregoing three types (Types I to III) of hernia by the presence of a separate extrahiatal diaphragmatic defect with intervening normal crural muscle [
2,
3]. However, parahiatal hernia is extremely rare; the exact incidence of parahiatal hernia is not known. Only a few patients with this condition have been reported so far [
1,
2,
4‐
6]. Palanivelu
et al. [
1] reported that the incidence of parahiatal hernia in their study on fundoplication for paraesophageal hernia was 0.35%.
Parahiatal hernia is characterized by the presence of a separate extrahiatal diaphragmatic defect with intervening normal crural muscle. Moreover, the hiatus is structurally normal and both crural muscles are intact [
7,
8]. In our patient, the esophageal hiatus was normal, and the hernia defect was separated from the hiatus by the left crus of the diaphragm at laparoscopic findings. These findings supported the diagnosis of parahiatal hernia in our patient.
Incomplete obliteration of the embryonic pleuroperitoneal canal, resulting in a persistent pneumoenteric recess, has been theorized to explain the etiology of naturally occurring primary parahiatal hernias [
9]. Although these hernias may arise from both sides of the pneumoenteric recesses, they are usually found on the left side. This may be attributed to the presence of the liver on the right side, leading to protection of the diaphragm on that side [
2,
4‐
6]. However, the low incidence of this condition makes it difficult to draw firm conclusions. Secondary or acquired parahiatal hernia occurs as a result of protrusion of the gastric fundus through an intracrural defect, probably caused by disruption during crural repair for gastroesophageal reflux disease [
1]. Moreover, secondary parahiatal hernia is also known to occur after esophagectomy, probably because of excessive manipulation of the crural muscles [
10]. The secondary type is probably more common than the primary or congenital type. In our case, the left hemidiaphragm was not elevated before treatment of the left malignant pleural mesothelioma, whereas an elevation was observed after treatment. From these facts, we hypothesized that the mesothelioma developed at a fragile site of the left diaphragm, such as the left pneumoenteric recess, which then may have caused the hernial orifice in our patient. Papavramidis
et al. described that chronically increased intra-abdominal pressure (IAP) leads to both morphological and biochemical adaptations of the costal diaphragm [
11]. Chronic IAP, such as obesity and ascites and so on, was reported to play an important role in the causes of a hernia at the weak point of the abdominal cavity [
12,
13]. Because there were no clear causes of increase in IAP in our case, a discrepancy in pressure between the thoracic and abdominal cavities may have contributed to the development of this hernia. Moreover, the biopsy of pleura for mesothelioma also may result in the creation of a hernia orifice. Therefore, we diagnosed the patient with secondary (or iatrogenic) parahiatal hernia in our case.
On the one hand, laparoscopic repair for paraesophageal hernia has become widely recognized [
14,
15]. On the other hand, the number of reported cases of parahiatal hernia treated by laparoscopic surgery has increased gradually [
1,
2,
4]. The procedures of hernia repair include primary repair or the use of a mesh. Rodefeld
et al. [
2] reported a case in which it was possible to perform the continuity hernia repair laparoscopically. They added laparoscopic Nissen fundoplication to reduce the risk of gastric volvulus in case of hernia recurrence. Scheidler
et al. [
4] reported a case in which both laparoscopic closure of a parahiatal hernia and standard Nissen fundoplication were performed. In their case, the normal location of the esophagogastric junction was revealed in a barium contrast study. Moreover, a preoperative esophageal manometric study revealed normal esophageal body peristalsis and normal resting pressure and length of the lower esophageal sphincter. The use of additional fundoplication as a prophylactic measure during the treatment of parahiatal hernia remains controversial because of the low incidence rate of this condition.