Bochdalek Hernia

Etiology

Environmental and genetic factors have been postulated to contribute to the etiology of a Bochdalek hernia. An estimated 30% of CDHs are attributable to genetic causes, such as chromosomal anomalies, copy number, and sequence variants. The aforementioned affected genes discovered include multiple transcription factors and the retinoic acid pathway. Most appear to have pleiotropic effects and variable penetrance, causing a range of phenotypes. As expected, a developmental anomaly in 1 organ often correlates with developmental anomalies elsewhere, and Bochdalek hernias are no exception. Multisystem genetic syndromes and associations, such as pulmonary and cardiac defects, are identified.[1]

Epidemiology

CDH is a congenital anomaly of the diaphragm with an incidence of approximately 1 in 2000 to 1 in 3000 births. Of those, roughly 70% to 75% are posterolateral defects and, thus, are characterized as Bochdalek hernias.[2] In a population-based cohort study of statewide diagnoses of CDHs in Utah, CDH occurred in 1 in 3156 births. There is a predilection in men with a man-to-woman ratio of 1.72 to 1. Of these, 64% of the cases were isolated, 23% were multiples (additional unrelated major malformations or unique minor malformations), and 13% were syndromic.[3] Symptomatic Bochdalek hernias in adults are relatively rare, with most cases found incidentally.[4][5] The overall incidence of adults with asymptomatic Bochdalek hernias has been estimated to be as low as 0.17% and as high as 6%.[6] However, there is a school of thought that some of these were hernias acquired during adulthood.[7][8]

Pathophysiology

The pathophysiology of Bochdalek hernias and CDHs, in general, is poorly understood. A Bochdalek hernia is congenital due to a developmental defect in the diaphragm formation. At approximately 4 weeks of gestation in humans, the diaphragm forms from several infoldings. Anteriorly, the central tendon is proposed to form from the septum transversum; posterolateral infoldings form the pleuroperitoneal membranes. The pleuroperitoneal canal, in turn, communicates between the pleural and peritoneal cavities via the foramen of Bochdalek at the posterior aspect of the developing diaphragm. This communication usually closes around week 8 of gestation.[9] Failure to do so results in a characteristic defect. Since the right canal closes before the left canal, most Bochdalek hernias (85%) are left-sided.[10]

Herniation of abdominal contents into the thoracic cavity can interfere with the normal development of the lungs; this can result in a varying degree of pulmonary hypoplasia and persistent pulmonary hypertension (PPH).[9] Thus, most symptomatic Bochdalek hernias are diagnosed at a younger age in children with respiratory symptoms. Presentation of Bochdalek hernia in adulthood is relatively rare and is typically manifested as gastrointestinal symptoms related to the herniated organ.[7] 

History and Physical

Bochdalek hernias tend to present differently in pediatric and adult age groups. In the pediatric age group, the presentation often includes respiratory symptoms from lung hypoplasia after mechanical compression of developing lung parenchyma in utero. In contrast, Bochdalek hernias in adults are usually asymptomatic and incidentally found. Symptoms in adults often manifest as vague or nonspecific gastrointestinal complaints.[7] [10] During the physical exam, findings could include auscultation of bowel sounds in the chest. More severe cases could show a scaphoid abdomen, as bowel contents herniate into the thorax.

A recent meta-analysis of 173 articles met the predefined inclusion criteria, encompassing 192 patients (50.5% men) with an average age of 45.41 ± 20.26 years. The predominant symptoms were abdominal pain (62.0%) and pulmonary issues (41.1%). The hernias most commonly protruded through the left side of the diaphragm (70.7%), with the large intestine (42.7%) and stomach (37.1%) being the most frequently herniated organs. The majority of patients (53.8%) underwent an open surgical procedure, with the abdominal approach being preferred (64.8%) over the thoracic approach. Postoperative complications within 30 days occurred in 21.5% of patients, and the 30-day mortality rate was 4.4%.[11]

Evaluation

Ultrasonography, plain film chest radiography, and thin section computed tomography (CT) with multiplanar reformats all play a role in diagnosing a Bochdalek hernia. Recently, magnetic resonance imaging (MRI) studies have also been used to evaluate these pathologies. A CDH is the most commonly reported indication for thoracic prenatal MRI.[12] Antenatal ultrasounds can demonstrate features that suggest CDHs, such as intrathoracic stomach bubble and mediastinal shift away from the herniated viscera. Postnatally, ultrasonography can delineate the entire diaphragm, assess for discontinuity, and evaluate the viscera that has herniated.[10] In plain film radiography, Bochdalek hernias are diagnosable by assessing for gas-filled loops of the bowel or a soft tissue mass above the level of the diaphragm. However, plain film chest radiography sensitivity is low, and CDHs can be confused with other thoracic pathology.

As such, thin-section CT with multiplanar reformats has become the industry standard for diagnosis due to increased sensitivity and ability to evaluate associated congenital anomalies. On CT of the chest, one can more accurately assess for focal defects in the diaphragm. CT was reported to have sensitivities of 78% for left-sided hernias and 50% for right-sided hernias.[13] 

Treatment / Management

Katsaros et al highlights the critical need for timely surgical intervention in patients with Bochdalek hernia to prevent life-threatening complications. In adults, these hernias can go undetected and become surgical emergencies if abdominal organs become strangulated, resulting in conditions like intestinal obstruction or gastric volvulus. Surgical repair is the only effective treatment for Bochdalek hernia in adults, preventing long-term complications and improving quality of life. Experienced surgeons often prefer a laparoscopic approach due to its minimal invasiveness and quicker recovery time.[11][14] (A1)

Antenatally, expected management and surveillance for complications is the standard of care. Sometimes, in severe herniation, fetoscopic endoluminal tracheal occlusion (FETO) therapy can be considered. This procedure temporarily blocks the trachea, and preliminary research suggests it improves lung development. Postnatally, management of hypoplastic lung tissue and maldevelopment takes precedence; this includes gentle ventilation, high-frequency oscillatory ventilation (HFOV), and extracorporeal membrane oxygenation (ECMO) therapies. PPH is also a sequela of CDH and mechanical compression of the lung during development. Treatment of PPH is usually inhaled nitric oxide and sildenafil.[2]

Differential Diagnosis

CDHs, such as Bochdalek hernias, are the most commonly reported anomaly of the diaphragm detected in utero. However, there are other diagnostic considerations, such as congenital diaphragmatic eventration, diaphragmatic paralysis, and extralobar pulmonary sequestration, which are detectable during pregnancy. Congenital diaphragmatic eventration is considered secondary to defective development of the diaphragmatic musculature with subsequent focal thinning. On the other hand, extralobar pulmonary sequestration is lung parenchyma with a separate pleural and vascular supply.[12] Diaphragmatic rupture or other sources of acquired diaphragmatic hernia should be considered in adults.

Prognosis

Overall survival rates vary across the literature, with most population-based studies suggesting an overall mortality rate between 42% and 68%.[2] However, single-institution studies suggest a survival rate of upwards of 90%.[15] This difference in survival rates is sometimes attributed to 'hidden mortality,' which considers the intrauterine deaths before arrival at the reporting institution. Some research suggests there has been an overall increase in patient survival. This is thought secondary to advances in critical care.[16] 

Complications

As mentioned, survivors with a Bochdalek hernia and CDH often demonstrate pulmonary symptoms with chronic lung disease but also gastroesophageal reflux disease (GERD), chest wall deformity, poor growth, and hernia recurrence. A high incidence of chronic lung disease is demonstrated in CDH survivors, which includes PPH and pulmonary hypoplasia, the latter of which can cause a restrictive lung defect; also, there is a high oxygen concentration requirement and subsequent ventilator-induced injury and even bronchopulmonary dysplasia in these patients. Other pulmonary morbidities include reactive airway disease, reduced airway disease, and recurrent lung infections. Many of these patients demonstrate improved pulmonary function to near normal in adulthood, though some adult survivors show persistent impairment on pulmonary function testing.[16]

Neurodevelopmental deficits may also occur in CDH survivors, which include, but are not limited to, neuropathological lesions (such as periventricular leukomalacia), cognitive and motor dysfunction, and emotional or behavioral problems. GERD and failure to thrive are the most common gastrointestinal impairment at approximately 50% to 100% and 50% to 60%, respectively. Musculoskeletal abnormalities such as pectus deformities and scoliosis have associations with CDH. Hernia recurrence has also been reported, with an increased defect size correlating with an increased risk for recurrence. The recurrence rate for patch repairs is estimated at 27% to 41% compared to 4% to 13% for primary repairs.[16]