Congenital pericardial absence is due to premature atrophy of the left common cardiac vein with insufficient blood supply to the pleuropericardium leading to its agenesis. Male/female ratio is 3:1 .This entity was described in the context of different syndromes₄,₅,₆,₇. HLA typing in straight back syndrome indicates that it is inherited as an autosomal dominant condition and suggested that the antigenic determinants may be located on chromosome 6₁.

Congenital absence of the pericardium is an uncommon finding ((1/10,000 in autopsies) comprise partial left (70%), partial right (17%) or total bilateral (extremely rare) pericardial absence₂). Most patients are asymptomatic are discovered incidentally during cardiac surgery for an unrelated condition or at postmortem examination. Symptomatic patients may experience non-exertional paroxysmal stabbing chest pain ₈. However homolateral cardiac displacement and augmented heart mobility impose an increased risk for traumatic aortic dissection₉. Partial left sided defects can be complicated by cardiac strangulation caused by herniation of the left atrial appendage, atrium or ventricle through the defect (chest pain, shortness of breath, syncope, or sudden death). About 30% of patients have additional congenital abnormalities₄,₅,₆,₇.Partial absence of pericardium is often associated with other cardiac anomalies including atrial septal defect ,bicuspid aortic valve ,mitral valve stenosis, patent ductus arteriosus , tetralogy of Fallot or pulmonary malformation. Coexistence with recurrent pulmonary infections₂ and endocarditis₁₀ are also reported.

On the contrary, straight back syndrome usually comes to attention due to cardiac murmurs. Referring diagnosis include atrial septal defect, pulmonic stenosis and rheumatic heart disease. In one study half the patients were asymptomatic; others had dyspnea after brisk effort, palpitation and atypical chest pain₁₁.

In patients suffering from pericardial absence clinical examination may show a significantly displaced apical impulse, which may be palpated in the anterior or midaxillary line. Basal ejection murmurs, apical midsystolic clicks and murmurs may also be found. Increased splitting of the second heart sound may be due to the presence of a right bundle branch block that is frequently associated with this defect₁₂.

In straight back syndrome decrease in antero-posterior chest dimensions due to loss of thoracic kyphosis. Other findings in order of frequency are: palpable pulmonary artery pulsation, ejection systolic murmurs in pulmonic area, palpable impulse in left lower sternal border, accentuation and delay in tricuspid valve closure, exaggerated inspiratory splitting of the second heart sound, increase in amplitude of aortic and pulmonary closure. None of patients had thrill in pulmonic area nor did any of them have diastolic murmurs₁₁.Apical systolic click and murmurs are usually due to coexistent mitral valve prolapse ₁₃.

Electrocardiographic manifestations of pericardial absence are: bradycardia, right bundle branch block, poor R-wave progression secondary to leftward displacement of the precordial transitional zone, and prominent P-waves in the mid-precordial leads which denote right atrial overload₈.

ECG manifestations of straight back syndrome are right bundle branch block in V₁ and small terminal r waves in aV_{R 11}.

Chest X-ray findings due to pericardial absence are levoposition of the heart, flattening and elongation of the left ventricular border, and a lucent area between the diaphragm and the heart, or aorta and pulmonary artery due to lung interposition.

Surprisingly patients with straight back syndrome may have some findings in the Chest X ray: pancake appearance simulating cardiomegaly, levoposition of heart, prominence of the main pulmonary artery₁₃. In all patients both the antero-posterior diameter and the ratio of antero-posterior to transthoracic diameter were below the normal mean ₁₁. On the lateral chest radiograph the distance from the middle of the anterior border T₈ to a vertical line connecting T₄ and T₁₂ was found to be significantly reduced compared to controls, and a value less than 1·2 cm is the established criteria for straight back₁.

Due to pericardial absence heart forms a “teardrop” appearance due to elongated atria and relatively bulbous ventricles because of suspension of the heart from its basal pedicle₁₄. Findings in order of decreasing frequency are: unusual windows (a higher and more lateral window is required), cardiac hypermobility (cardioptosis), abnormal swinging motion, paradoxical or flat systolic motion of the ventricular septum with normal systolic thickening ₁₅. Right ventricular overload with reduction in right atrial dimension may be evident with decreased tricuspid valve excursion. Increased diastolic wave velocities in both the superior vena cava and pulmonary veins on Doppler examination with decreased caval systolic wave velocity suggest accentuation of changes in systemic over pulmonary venous return₁₆ (esp. in partial defects).

Echocardiograms were normal in 36% and abnormal in 64% of patients (mitral valve prolapse (MVP) in (58%) and bicuspid aortic valve in (6%)) of patients with straight back syndrome₁₃. Strong association of MVP with this syndrome was proposed previously₁₇.One of the important issues on the long-axis view of tomographic echocardiography is the aorto-septal angle of patients with straight back syndrome which was wide and thought to be due to clockwise rotation of the heart rather than right ventricular enlargement₁₈.

ECG -gated MRI and spiral chest CT-scan are two other diagnostic tools to diagnose pericardial absence₁₉.ECG gated T₁ weighted spin echo magnetic resonance image is highly sensitive and is capable of demonstrating the absence of the preaortic pericardial recess in pericardial absence which is present in normal hearts₈,₁₉.

Complete cases of pericardial absence require no intervention unless complications occur. Patients with debilitating symptoms may benefit from pericardioplasty. However, in partial defects, when herniation occurs or is threatened, extension of the defect by the pericardiectomy, or pericardioplasty may be preformed₂,₈ but in straight back syndrome therapy is directed toward specific coexisting conditions (e.g. MVP).