Congenital diaphragmatic hernia in the neonatal period: review of 21 years' experience

Quantitative Measures of Right Ventricular Size and Function by Echocardiogram Correlate with Cardiac Catheterization Hemodynamics in Congenital Diaphragmatic Hernia

OBJECTIVE

To evaluate associations between cardiac catheterization (cath) hemodynamics, quantitative measures of right ventricular (RV) function by echocardiogram, and survival in patients with congenital diaphragmatic hernia (CDH).

STUDY DESIGN

This single-center retrospective cohort study enrolled patients with CDH who underwent index cath from 2003 to 2022. Tricuspid annular plane systolic excursion z score, RV fractional area change, RV free wall and global longitudinal strain, left ventricular (LV) eccentricity index, RV/LV ratio, and pulmonary artery acceleration time were measured from preprocedure echocardiograms. Associations between hemodynamic values, echocardiographic measures, and survival were evaluated by Spearman correlation and Wilcoxon rank sum test, respectively.

RESULTS

Fifty-three patients (68% left-sided, 74% liver herniation, 57% extracorporeal membrane oxygenation, 93% survival) underwent cath (39 during index hospitalization, 14 later) including device closure of a patent ductus arteriosus in 5. Most patients (n = 31, 58%) were on pulmonary hypertension treatment at cath, most commonly sildenafil (n = 24, 45%) and/or intravenous treprostinil (n = 16, 30%). Overall, hemodynamics were consistent with precapillary pulmonary hypertension. Pulmonary capillary wedge pressure was >15 mm Hg in 2 patients (4%). Lower fractional area change and worse ventricular strain were associated with higher pulmonary artery pressure while higher LV eccentricity index and higher RV/LV ratio were associated with both higher pulmonary artery pressure and higher pulmonary vascular resistance. Hemodynamics did not differ based on survival status.

CONCLUSIONS

Worse RV dilation and dysfunction by echocardiogram correlate with higher pulmonary artery pressure and pulmonary vascular resistance on cath in this CDH cohort. These measures may represent novel, noninvasive clinical trial targets in this population.

Outcomes of neonatal congenital diaphragmatic hernia in a non-ECMO center in a middle-income country: a retrospective cohort study

BACKGROUND

Most studies examining survival of neonates with congenital diaphragmatic hernia (CDH) are in high-income countries. We aimed to describe the management, survival to hospital discharge rate, and factors associated with survival of neonates with unilateral CDH in a middle-income country.

METHODS

We retrospectively reviewed the medical notes of neonates with unilateral CDH admitted to a pediatric intensive care unit (PICU) in a tertiary referral center over a 15-year period, from 2003-2017. We described the newborns' respiratory care pathways and then compared baseline demographic, hemodynamic, and respiratory indicators between survivors and non-survivors. The primary outcome measure was survival to hospital discharge.

RESULTS

Altogether, 120 neonates were included with 43.3% (52/120) diagnosed antenatally. Stabilization occurred in 38.3% (46/120) with conventional ventilation, 13.3% (16/120) with high-frequency intermittent positive-pressure ventilation, and 22.5% (27/120) with high frequency oscillatory ventilation. Surgical repair was possible in 75.0% (90/120). The overall 30-day survival was 70.8% (85/120) and survival to hospital discharge was 66.7% (80/120). Survival to hospital discharge tended to improve over time (p > 0.05), from 56.0% to 69.5% before and after, respectively, a service reorganization. For those neonates who could be stabilized and operated on, 90.9% (80/88) survived to hospital discharge. The commonest post-operative complication was infection, occurring in 43.3%. The median survivor length of stay was 32.5 (interquartile range 18.8-58.0) days. Multiple logistic regression modelling showed vaginal delivery (odds ratio [OR] = 4.8; 95% confidence interval [CI] [1.1-21.67]; p = 0.041), Apgar score [Formula: see text] 7 at 5 min (OR = 6.7; 95% CI [1.2-36.3]; p = 0.028), and fraction of inspired oxygen (FiO₂) < 50% at 24 h (OR = 89.6; 95% CI [10.6-758.6]; p < 0.001) were significantly associated with improved survival to hospital discharge.

CONCLUSIONS

We report a survival to hospital discharge rate of 66.7%. Survival tended to improve over time, reflecting a greater critical volume of cases and multi-disciplinary care with early involvement of the respiratory team resulting in improved transitioning from PICU. Vaginal delivery, Apgar score [Formula: see text] 7 at 5 min, and FiO₂ < 50% at 24 h increased the likelihood of survival to hospital discharge.

Right Ventricular Strain, Brain Natriuretic Peptide, and Mortality in Congenital Diaphragmatic Hernia

Rationale: Brain-type natriuretic peptide (BNP) correlates with pulmonary hypertension as demonstrated by echocardiogram in congenital diaphragmatic hernia (CDH); however, its association with right ventricular (RV) function and mortality is unknown.Objectives: To characterize the relationships between echocardiogram-derived RV strain, BNP, and mortality in diaphragmatic hernia.Methods: We performed a single-center retrospective cohort study of infants with CDH and at least one BNP-echocardiogram pair within a 24-hour period. RV global longitudinal strain (GLS) and free-wall strain (FWS) were measured on existing echocardiograms. Associations among strain, BNP, and mortality were tested using mixed-effect linear and logistic regression models. Survival analysis was stratified by BNP and strain abnormalities.Results: There were 220 infants with 460 BNP-echocardiogram pairs obtained preoperatively (n = 237), ≤1 week postoperatively (n = 35), and >1 week postoperatively ("recovery"; n = 188). Strain improved after repair (P < 0.0001 for all periods). Higher BNP level was associated with worse strain in recovery but not before or immediately after operation (estimate [95% confidence interval] for recovery: GLS, 1.03 [0.50-1.57]; P = 0.0003; FWS, 0.62 [0.01-1.22]; P = 0.047). BNP and strain abnormalities were associated with an extracorporeal-membrane oxygenation requirement. Higher BNP level in recovery was associated with greater mortality (odds ratio, 11.2 [1.2-571.3]; P = 0.02). Abnormal strain in recovery had high sensitivity for detection of mortality (100% for GLS; 100% for FWS) but had low specificity for detection of mortality (28% for GLS; 48% for FWS).Conclusions: Persistent RV dysfunction after CDH repair may be detected by a high BNP level and abnormal RV strain.

The Outcome of Operated Neonates with an Isolated Congenital Diaphragmatic Hernia in a Limited Resource Scenario: A Critical Analysis

Introduction

Congenital diaphragmatic hernia (CDH) is one of the most common neonatal emergencies, and the ideal current therapy requires high standards of neonatal care and advanced facilities. However, majority of neonates born with CDH are treated in public sector hospitals, with limitations in resources and workforce.

Objectives

The aim of the study was to review and analyze the outcome of operated neonates with isolated CDH in a public sector hospital and medical college where a standard protocol of management was followed, considering the need for optimization of therapy in view of the resource constraints.

Materials and Methods

A retrospective chart review and analysis of the antenatal, preoperative, operative, and postoperative records of all neonates with operated CDH during the 3-year period from June 2015 to June 2018 at the hospital was done. The standard institutional protocol being followed included preoperative stabilization, risk stratification for patient selection, early decision regarding operative intervention, and continued postoperative ventilation.

Results

During the 3-year period, 78 children were admitted with CDH, of which 40 newborns with operated CDH were studied. The mean age at surgery was 72 h. Thirty-five of these 40 cases (87.5%) made an uneventful recovery, while mortality was 5/40 (12.5%). All mortalities (5/40) occurred during the postoperative period after 3 days due to respiratory failure while being ventilated.

Conclusion

The strategy of a uniform protocol in the management of CDH adapted to the practical constraints of the institution yielded good results in the low-to-moderate risk group of neonatal CDH. The approach also facilitated the segregation of high-risk cases and optimal utilization of available facilities in a limited resources scenario.

Prevalence and risk factors for congenital diaphragmatic hernia: A global view

PURPOSE

To determine the global prevalence for congenital diaphragmatic hernia (CDH) and identify CDH-related risk factors.

METHODS

Using a defined strategy, a systematic review of the literature was conducted according to PRISMA guidelines, searching for population-based epidemiological studies to evaluate the prevalence of CDH globally and per country. Studies containing overlapping populations or timeframes were excluded. CDH-related risk factors were calculated by meta-analysis using RevMan5.3 and expressed as risk ratio and 95% confidence interval.

RESULTS

Prevalence: Of 8230 abstracts screened, 30 full-text articles published between 1980 and 2019 were included. The overall prevalence of CDH was 2.3 in 10,000 births (16,710 CDH babies in 73,663,758 livebirths).

RISK FACTORS

From 9 studies we found that male sex [RR 1.38 (1.05-1.80), p=0.02] and maternal age >35 years [RR 1.69 (1.26-2.25), p=0.0004] were associated with CDH. Conversely, maternal black ethnicity resulted as a protective factor [RR 0.82 (0.77-0.89, p<0.00001].

CONCLUSION

This study reveals that there is a worldwide paucity of population-based studies, and those studies that report on prevalence and risk factors come from a small number of countries. The prevalence of CDH varies within and across geographical world regions. The main risk factors for CDH identified are male sex and older maternal age. More epidemiological studies, involving more world regions, are needed to identify possible strategies to help strengthen our understanding of the risk factors, provide clinicians with the tools necessary for prenatal and postnatal counseling, and inform policy makers on how to strategize CDH care in different parts of the world.

TYPE OF STUDY

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Level III.

[Congenital diaphragmatic hernia: a condition which is not always easy to diagnose]

Congenital hernia of the diaphragmatic dome (CDC) is a congenital embryopathy where all or part of the diaphragmatic dome fails to form. Its rate is 1/3500 live births with a male predominance. This study reports a case of Bochdalek hernia as well as data in the literature and highlights the diagnostic and therapeutic challenges in this disease. Diagnosis and antenatal management are essential to reduce patient's mortality and morbidity. Prognosis is poor and depends on the presence and degree of pulmonary hypoplasia and on the association with congenital malformations.

Congenital heart disease associated with congenital diaphragmatic hernia: A systematic review on incidence, prenatal diagnosis, management, and outcome

PURPOSE

The purpose of this study was to evaluate the impact of congenital heart disease (CHD) on infants with congenital diaphragmatic hernia (CDH).

METHODS

Using a defined search strategy (PubMed, Cochrane, Embase, Web of Science MeSH headings), we searched studies reporting the incidence, management, and outcome of CDH infants born with associated CHD.

RESULTS

Of 6410 abstracts, 117 met criteria. Overall, out of 28,974 babies with CDH, 4427 (15%) had CHD, of which 42% were critical. CDH repair was performed in a lower proportion of infants with CHD (72%) than in those without (85%; p < 0.0001). Compared to CDH babies without CHD, those born with a cardiac lesion were more likely to have a patch repair (45% vs. 30%; p < 0.01) and less likely to undergo minimally invasive surgery (5% vs. 17%; p < 0.0001). CDH babies with CHD had a lower survival rate than those without CHD (52 vs. 73%; p < 0.001). Survival was even lower (32%) in babies with critical CHD.

CONCLUSION

CHD has a strong impact on the management and outcome of infants with CDH. The combination of CDH and CHD results in lower survival than those without CHD or an isolated cardiac defect. Further studies are needed to address some specific aspects of the management of this fragile CDH cohort.

TYPE OF STUDY

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Level III.

A Clinical Study on Congenital Diaphragmatic Hernia in Neonates: Our Institutional Experience

Background:

Congenital diaphragmatic hernia (CDH) is a complex developmental defect having a multifactorial etiology; i majority of cases (~80%), the cause is not known. Survival rates for patients with CDH have increased over the past decade with early prenatal detection and better postnatal management including surgery. Clinical profile and the outcome of 83 CDH neonates were studied and analyzed over a period of 12 years in our institute.

Aims and Objectives:

The clinical study was to analyze the clinical profile and outcome of CDH among the neonates in a tertiary care referral neonatal and pediatric center in Karnataka, India.

Materials and Methods:

This was a retrospective and prospective observational study conducted from January 2005 to March 2017, over a period of 12 years in a tertiary care referral neonatal and pediatric center in southern India. Clinical characteristics and risk factors of 83 neonates admitted and diagnosed with CDH were compared between survivors and nonsurvivors both preoperatively and postoperatively. Neonates with clinical and intraoperative diagnosis of diaphragmatic eventration were not included in this study. Multivariate logistic regression analysis was performed to determine independent predictors for mortality.

Results:

A total of 83 neonates admitted and diagnosed with CDH were included in this study; 73 of them underwent surgical repair. The total survival rate in neonates with CDH was 70/83 (84.33%) and the overall operative mortality was 3/73 (4.1%). There was a significant difference between CDH neonates who survived 70/83 (84.33%) and those who died 13/83 (15.67%), in the age on admission, 5 min Apgar score, onset of respiratory distress, preoperative ventilation, the presence of persistent pulmonary hypertension of the newborn (PPHN), high-frequency oscillatory ventilation (HFOV), and length of hospital stay with P < 0.05. Using multivariate logistic regression analysis, the following factors independently predicted mortality: onset of respiratory distress in hours (odds ratio: 0.5, 95% confidence interval: 0.37–0.82) and preoperative ventilation (odds ratio: 0.02; 95% confidence interval: 0.0028–0.1558). When we compared CDH neonates who survived after surgery (n = 70) with those who expired (n = 3) postoperatively, there was a significant difference in the gestational age in weeks, side of CDH, PPHN, HFOV and length of hospital stay with P < 0.05.

Conclusion:

CDHs are common on the left side with fairly good prognosis. Though, the right-sided CDH are rare; they do carry a good prognosis, as it was seen in our experience.

Trends in treatment and in-hospital mortality for neonates with congenital diaphragmatic hernia

OBJECTIVE

We performed a retrospective cohort study in order to examine recent trends in use of post-partum treatments and in-hospital mortality for congenital diaphragmatic hernia (CDH).

STUDY DESIGN

Included were infants with CDH, born in 2003 to 2012 and hospitalized at ⩽7 days of age at one of 33 United States tertiary referral children's hospitals with extracorporeal membrane oxygenation (ECMO) programs. In-hospital mortality as well as use of ECMO, surfactant and a variety of vasodilators were examined for trends during the study period.

RESULT

Inclusion criteria were met by 3123 infants with CDH. Among 2423 term or near-term infants, odds of death decreased annually for those with isolated or complex CDH. For 700 premature or low-birth weight infants with CDH, in-hospital mortality did not change. Among treatments for CDH, increasing with time in the study cohort were use of milrinone and sildenafil individually, and use of multiple vasodilators during the hospitalization.

CONCLUSION

Survival improved in large subgroups of term or near-term infants with CDH in this 10-year multicenter cohort, temporally associated with increasing use of multiple vasodilators. Use of vasodilators for infants with CDH is increasing despite a lack of evidence supporting efficacy or safety. Prospective research is needed to clarify specific causal effects contributing to improving survival in these infants.

Clinical characteristics and outcomes of patients with right congenital diaphragmatic hernia: A population-based study

PURPOSE

The purpose of this study was to compare RCDH to LCDH from the perspective of prenatal diagnosis, illness severity, treatment, and outcome.

METHODS

A retrospective study of all cases of CDH registered in the Canadian Pediatric Surgery Network (CAPSNet) database from 2005 to 2013 was conducted. Side of defect comparisons were made by prenatal diagnostic features, birth demographic data, intensity of medical treatment, timing and type of surgery, and outcomes. Outcomes prediction with logistic regression modeling using side of defect as an exploratory covariate was performed.

RESULTS

The study cohort included 498 patients, of which 84 (17%) cases had RCDH. Prenatal diagnosis was more commonly made for LCDH. No difference existed in perinatal risk factors (GA, illness severity (SNAP-II) score, associated anomalies), preoperative treatment intensity (use of vasodilators, inotropes), timing of surgery, ventilation days, need for ECMO, LOS, and overall survival. Significant differences between RCDH and LCDH were detected for patch repair rate (48.2% vs. 30.6%; p=0.036) and recurrence (4.1% vs. 0.6%; p=0.038). Stepwise regression modeling identified side of hernia as independently predictive of need for patch.

CONCLUSIONS

Overall, little difference exists between RCDH and LCDH in terms of prognostic factors and outcomes.

An evidence-based review of the current treatment of congenital diaphragmatic hernia

Congenital diaphragmatic hernia is a rare but severe condition affecting 1 in 2000 to 3000 newborns with a survival rate of 67%. Although regular antenatal screening allows prenatal diagnosis in many cases, traditionally treatment has been based on postnatal surgical repair. Recent literature has pointed out the survival benefits of initial stabilization and the use of gentle ventilation strategies prior to definitive treatment, shifting the trend from immediate to delayed surgical repair. Advances in fetal intervention have allowed the introduction of fetal endoscopic tracheal occlusion as a method to hasten lung development before birth in order to minimize postnatal morbidity. Despite appropriate treatment, the long-term outcomes of these patients are plagued with numerous complications, associated with the primary pathology and also aggressive therapeutic measures. International centers of excellence have recently come together in an effort to standardize the care of such patients in hopes of maximizing their outcomes.

Prematurity, asphyxia and congenital malformations underrepresented among neonates in a tertiary pediatric hospital in Vietnam

BACKGROUND

Estimated 17,000 neonates (≤ 28 days of age) die in Vietnam annually, corresponding to more than half of the child mortality burden. However, current knowledge about these neonates is limited. Prematurity, asphyxia and congenital malformations are major causes of death in neonates worldwide. To improve survival and long term development, these vulnerable neonates need access to the specialized neonatal care existing, although limited, in lower middle-income countries like Vietnam. The aim of this study was to describe these conditions in a specialized Vietnamese hospital, compared to a Danish hospital.

METHODS

We performed a comparative observational study of all neonates admitted to a tertiary pediatric hospital in South Vietnam in 2009-2010. The data were prospectively extracted from the central hospital registry and included basic patient characteristics and diagnoses (International Classification of Diseases, 10th revision). Prematurity, asphyxia and designated congenital malformations (oesophageal atresia, gastroschisis, omphalocoele, diaphragmatic hernia and heart disease) were investigated. In a subgroup, the prematurity diagnosis was validated using a questionnaire. The hospitalization ratio of each diagnosis was compared to those obtained from a Danish tertiary hospital. The Danish data were retrieved from the neonatal department database for a ten-year period.

RESULTS

The study included 5763 neonates (missing<1%). The catchment population was 726,578 live births. The diagnosis was prematurity in 7%, asphyxia in 2% and one of the designated congenital malformations in 6%. The diagnosis of prematurity was correctly assigned to 85% of the neonates, who were very premature or had very low birth weight according to the questionnaire, completed by 2196 neonates. Compared to the Danish Hospital, the hospitalization ratios of neonates diagnosed with prematurity (p<0.01), asphyxia (p<0.01) and designated congenital malformations (p<0.01- 0.04) were significantly lower.

CONCLUSION

Our findings suggest the investigated diagnoses were underrepresented in the Vietnamese study hospital. In contrast, relatively mild diagnoses were frequent. These results indicate the use of specialized care may not be optimal. Pre-hospital selection mechanisms were not investigated and additional studies are needed to optimise utilisation of specialized care and improve neonatal survival.

Newly designed bioabsorbable substitute for the treatment of diaphragmatic defects

PURPOSE

Earlier studies have investigated the suitability of various materials and autologous grafts for the repair of diaphragmatic defects. Our group investigated the feasibility of using an artificial diaphragm (AD) to repair wide diaphragmatic defects.

METHODS

Twelve pigs were laparotomized and, in each pig, a defect was fashioned by resecting a round 8-cm diameter hole in the left diaphragm. Next, the defect was repaired by implanting an AD. The animals were relaparotomized 8 or 24 weeks after implantation for gross, histological and radiological observation of the implanted sites.

RESULTS

All recipient animals survived until killing for evaluation. Chest X-ray examinations showed no differences between the preoperative diaphragms and the grafted diaphragms at 8 and 24 weeks after implantation. At 8 weeks after implantation, the implanted sites exhibited fibrous adhesions to the liver and lungs without deformities or penetrations. Parts of the surface tissue at the graft sites had a varnished appearance similar to those of the native diaphragm. Histology performed at 8 weeks detected no trace of the ADs in the graft sites; however, numerous inflammatory cells and profuse fibrous connective tissue were observed. At 24 weeks after implantation, no differences were found in the thorax between the areas with the grafts and the unaffected areas. Histology of the graft sites in the thorax confirmed growth of mesothelial cells similar to that observed in the native diaphragm.

CONCLUSIONS

Artificial diaphragms can be a novel substitute for diaphragmatic repair.

Mid-term differences in right ventricular function in patients with congenital diaphragmatic hernia compared with controls

BACKGROUND

Patients with congenital diaphragmatic hernia (CDH) may have abnormal lung development, which may cause detrimental effects on right ventricular (RV) function. This study aimed to determine if there are persistent echocardiographic differences in RV function in patients with CDH years after repair versus control patients.

METHODS

Patients who underwent repair for CDH were recruited. RV function was evaluated by strain analysis and tissue Doppler imaging (TDI). Wilcoxon's rank-sum test was used for analysis.

RESULTS

Seven CDH patients and 16 control patients were studied. There was no difference in age between the CDH and control groups (6.2±1.7 years vs. 5.7±1.7 years). TDI demonstrated significantly lower values in the RV early diastolic wave (12.8±1.5 cm/s vs. 16.1±3.1 cm/s) and RV systolic wave (10.2± 0.8cm/s vs. 13.4±1.3 cm/s) when comparing the CDH group and the control group. Interventricular apical septal strain was signifi cantly lower in the CDH group than in the control group (-20.1±4.6% vs. -25.4±4.1%). There was a trend towards lower strain values in the RV mid-lateral segment in the CDH group (-30.8±9.9% versus -39.7±6.0%, P=0.06) and a lower global RV strain (-27.8±3.0% vs. -31.1±3.1%, P=0.06).

CONCLUSIONS

Patients who underwent CDH repair continue to have differences in RV function years after repair. Follow-up is needed to determine how these differences impact cardiac function in adult survivors of CDH.

Permissive hypercapnia in the management of congenital diaphragmatic hernia: our institutional experience

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a potentially lethal anomaly associated with pulmonary hypoplasia and persistent pulmonary hypertension. Permissive hypercapnia is a strategy designed to reduce lung injury from mechanical ventilation in infants. It has been shown to be a potentially superior method of ventilator management for patients with CDH. In 2001, the Divisions of Neonatology and Pediatric Surgery at the University of Virginia Children's Hospital established permissive hypercapnia as the management strategy for treatment of CDH. We hypothesized that permissive hypercapnia would be associated with improved outcomes in this patient population.

STUDY DESIGN

This retrospective review compares outcomes of infants treated for CDH in the extracorporeal membrane oxygenation (ECMO) era before and after initiation of permissive hypercapnia at a single institution. Outcomes were compared using univariate statistical analysis.

RESULTS

Ninety-one patients were available for analysis and were divided into 2 groups: 42 (Group 1) treated before and 49 (Group 2) treated after implementation of permissive hypercapnia. Survival was higher in Group 2 (85.8% vs 54.8%; p = 0.001; relative risk [RR] 3.17). Morbidity was lower in Group 2 and approached statistical significance (65.3% vs 83.3%; p = 0.052). Patients in Group 2 were repaired later, had a lower rate of ECMO use, and were extubated earlier. There was no difference in hospital stay.

CONCLUSIONS

The use of permissive hypercapnia for infants with CDH was associated with decreased mortality, a longer period of ventilation before repair with a shorter period of ventilation after repair, a lower rate of ECMO use, and no lengthening of hospital stay. Permissive hypercapnia remains the standard of care for ventilation of infants with CDH at our institution.

The embryology of the diaphragm

Despite the progress in prenatal diagnosis and intervention as well as postnatal therapeutic strategies, congenital diaphragmatic hernia (CDH) is still associated with a meaningful mortality because of the induced pulmonary hypoplasia. An essential key in understanding the pathogenesis of CDH is the underlying embryology, which has been neglected during the last decades. Likewise, the development of the normal diaphragm is still poorly understood. Obsolescent perceptions, mainly formed from histologic sections, are still propagated. In this review we present an atlas of scanning electron microscopy images that depict the normal and defective development of the diaphragm in the nitrofen rat model for CDH. Our findings suggest that the normal diaphragm mainly develops from the posthepatic mesenchymal plate. If the development of the posthepatic mesenchymal plate is impaired, a diaphragmatic defect occurs.

The diaphragm

This article discusses the diaphragm from a surgical perspective. Although it is a relatively simple organ compared with other structures, the diaphragm serves important anatomic and functional roles necessary for proper respiratory function. It is an organ of little irregularity or disease, and easily manipulated in the operating room by those who have a basic understanding of its anatomic details.