Anesthetic management in a case of congenital sternal cleft diagnosed incidentally on the operating table.

Congenital absence of sternum, also known as sternal cleft, is a rare anomaly. It is due to impaired organogenesis leading to nonfusion of sternal bars. It may be of two types- complete or incomplete. It may be associated with other congenital malformations viz., cardiac, anorectal etc., or may be a part of Cantrell's pentalogy. Besides cosmetic concerns, mediastinal structures are at increased risk to damage in case of trauma to the anterior chest wall. Due to restricted mediastinal space, there may be restrictive pulmonary dysfunctions and unstable hemodynamics. It usually presents in the neonatal period or early infancy, rarely in adult age. The defect should be surgically closed as early as possible. If cardiac arrest occurs due to any reason, the only option is open cardiac massage. We report a case of complete congenital sternal cleft accidentally diagnosed on the operation table, while preparing the patient for diagnostic laparotomy. The patient was retrospectively assessed for the presence of other congenital malformations.

INTRODUCTION

Congenital absence of the sternum is a rare anomaly. It is also known as congenital sternal cleft. It is due to failure of fusion of sternal bars in the midline, which routinely unite at 10 weeks of gestation. It may be of two types- complete or incomplete. Complete sternal cleft is rarer than incomplete one. It usually presents in early infancy or immediately after birth but infrequently the patient may come in adolescence due to cosmetic reasons. Very rarely it may be coincidentally diagnosed later at adult age. It may be associated with other congenital malformations viz., cardiac, anorectal etc., or may be a part of Cantrell's pentalogy. Besides cosmetic concerns, mediastinal structures are at increased risk to traumatic damage. Due to restricted mediastinal space there may be restrictive pulmonary functions and unstable hemodynamics particularly in the perioperative period. The defect should be surgically closed as early as possible. If cardiac arrest occurs due to any reason, the only option is open cardiac massage. Congenital anomalies often go unnoticed in the majority of patients who are asymptomatic and are incidentally diagnosed when they present for some other disease.

CASE REPORT

We report a rarest presentation of congenital sternal cleft of complete variety diagnosed coincidentally at adult age. It is a case of 35 years asthenic built female presenting with malaena, posted for diagnostic laparotomy. She was a mother of two children, normal vaginal delivery, which was uneventful. She never had any problem due to the defect besides the cosmetic concern about, which she was ignorant. She was illiterate and from poor rural background.

On examination, there was pallor. There was no cyanosis or clubbing. Arterial pulsations were clearly visible over the precordium with just a thin layer of skin covering it. On auscultation, no murmur could be heard. There was no evidence of any other defect of midline fusion of structures. Routine investigations revealed anemia. The anomaly was accidentally diagnosed on the operating table, while applying chest leads. In chest roentgenogram, the sternal shadow was absent, which could not be appreciated at the time of preoperative examination.

There was no history of cardiothoracic surgery neither any suture line over the precordium. We suspected it as a case of congenital absence of sternum. History revealed the defect was congenital, but asymptomatic. The computed axial tomography scan of chest done postoperatively confirmed the diagnosis.

Congenital absence of sternum can be associated with other congenital defects or it may be a part of Cantrell's pentology.[1] Although no murmur could be heard still we were worried about the presence of silent cardiac defect, which could become evident under anesthesia and reversal of shunt may be life-threatening. In our case, two-dimensional echocardiogram done postoperatively revealed small patent foramen ovale without significant shunt. Besides this, absence of sternum also causes decrease the intrathoracic space. Studies have reported that the heart is the least tolerant organ to reduced space inside the thoracic cage thus making these patients more susceptible to hemodynamic catastrophies.[23] Moreover, there could be the problem, while ventilating due to paradoxical respiration as a result of loss of ventral support of ribs and due to restrictive lung disorders.

In the operating room, routine monitoring viz., heart rate, electrocardiogram, noninvasive blood pressure, saturation of arterial blood (SpO2) was started. Radial artery was cannulated so as to monitor intrarterial blood pressure. Epidural catheter was secured in the lumbar region for perioperative analgesia. Right subclavian vein was catheterized and central venous pressure (CVP) guided intravenous (iv) fluids were given. Target was to maintain CVP of 6-8 cm H2O. Patient was co-loaded with 500 ml of injection hydroxyethyl starch.

Surgery was done under general anesthesia using drugs judiciously in calculated doses thus avoiding respiratory and cardiac depression. After preoxygenation for 5 min injection glycopyrrolate 0.2 mg iv, injection fentanyl 50 mcg iv and injection ondansetron 4 mg iv were given as premedicant. Anesthesia was induced with injection propofol 60 mg slowly just sufficient for the abolition of eyelash reflex. Endotracheal intubation was facilitated with injection rocuronium 30 mg iv. There was difficulty in maintaining SpO2 on spontaneous ventilation and the patient was immediately intubated. Anesthesia was maintained with oxygen: Air: Isoflurane since patient was not tolerating nitrous oxide. Neuromuscular blockade was achieved with injection vecuron iv. Just after induction, injection dexmedetomidine was started as continuous iv infusion in a dose of 0.2 mcg/kg and continued until 24 h after the completion of surgery.

Intraoperative period was uneventful; patient was hemodynamicaly stable and had smooth recovery. While exploring the gut, Meckel's diverticulum was found, which was excised and the defect repaired. There was no other defect in the gut. Patient was kept on elective mechanical ventilation 24 h postoperatively. Epidural infusion of injection ropivacaine 0.25% was started just after induction of anesthesia at 5 ml/h for perioperative pain relief and to decrease the intraoperative requirement of anesthetic agents.

Monitoring was continued in the postoperative period. Patient was stable postoperatively. She was shifted to intensive care unit and kept on elective mechanical ventilation for 24 h in the postoperative period. At the time of extubation, she was conscious comfortable responding to verbal commands and pain free. Infusion of dexmedetomidine was discontinued at the time of extubation. Ropivacaine infusion was continued until the 3rd postoperative day, epidural catheter removed and patient shifted to ward. The postoperative period was uneventful and she was discharged from hospital in the scheduled manner.

DISCUSSION

Congenital sternal cleft is classified as complete or incomplete, with complete cleft the rarer form[4] the incidence being (1:100,000). In embryonic life, the sternum has its origin in the lateral plate mesoderm of either side of midline, which become fused by the 10th weeks. Very rarely, the sternal bars fail to join in the midline, which results in a complete sternal cleft. The underlying mediastinal structures viz., heart and great vessels are left unprotected and may be easily injured by external trauma.[5]

The patient usually presents immediately after birth or early in infancy. Asymptomatic patients usually present for cosmetic reasons or are coincidentally diagnosed at a later age, as was in our case. The challenge to the anesthetist is the risk of paradoxical respiration especially if the defect is incomplete, risk of trauma to heart and great vessels while handling the patient etc., If cardiopulmonary resuscitation is required open cardiac massage is a must. Moreover, there may be associated congenital cardiac anomalies leading to severe cardiovascular compromise during anesthesia and if pulmonary hypertension is associated then it may be difficult to maintain adequate oxygenation of arterial blood.[6] In this case, there was presence of Meckel's diverticulum and patent foramen ovale.

The anomaly may be associated with defects in the anterior chest wall such as ectopia cordis, or, in Cantrell's pentalogy, with a combination of defects involving the abdominal wall, sternum, diaphragm, pericardium, and heart. It can be diagnosed in the prenatal period with three-dimensional ultrasonography.[7] Postnatal diagnosis is based on chest X-ray and etiology is supposed to be familial/teratogenic/nutritional.[8] Complete variety is associated with paradoxical respiration leading to repeated bouts of cyanosis and recurrent chest infections.[9] These patients usually present in early infancy for the primary cause. The defect should be surgically corrected as early as possible.