Screening helical computed tomographic scanning in haemodynamic stable patients with transmediastinal gunshot wounds☆☆☆

The general trauma surgeon is not infrequently faced with caring for patients with transmediastinal gunshot wounds (TMGSWs). Haemodynamic unstable patients require prompt resuscitation and immediate surgical intervention as they generally have major cardiac or vascular injuries. Haemodynamic stable patients, on the other hand, may have occult vascular, oesophageal, tracheobronchial or cardiac injuries. At our institution, traditionally, the evaluation of stable patients with TMGSWs has routinely included a chest radiograph, angiography, oesophography and cardiac ultrasound. Bronchoscopy is reserved for grossly symptomatic tracheobronchial injuries. These investigations are time-consuming, labour-intensive, somewhat invasive, often normal and in addition, expensive. Recent reports have suggested that contrast-enhanced helical computed tomography (CT) is as an effective screening tool for evaluating the missile track in haemodynamically stable patients with TMGSWs.3, 4, 5, 7 The purpose of this study was to review our experience with CT scanning in predicting potential mediastinal injuries in haemodynamically stable patients with TMGSWs.

Patients and methods 

All haemodynamically stable patients with TMGSWs admitted to the Trauma Unit at Groote Schuur Hospital (January 2002–May 2005 inclusive), were identified from a prospectively collected database and their charts reviewed. Haemodynamic stability was defined as a sustained systolic blood pressure greater than 100mmHg. Penetrating transmediastinal injury was defined as evidence of a single missile entry and exit on opposite sides of the thorax; missile entry and missile retention on opposite sides of the thorax, and missile entry on one side of the thorax with missile retention in the mediastinum.7 Initial assessment and resuscitation was according to Advanced Trauma Life Support® guidelines. Patient demographics, mechanism of injury, haemodynamic status, missile trajectory, diagnostic investigations and operative interventions performed, associated injuries, complications and survival were recorded. Towards the latter period of 2002, the institutional algorithm for patients with TMGSWs was changed to include a contrast-enhanced helical CT scan of the chest. A dynamic helical CT scan (single slice Siemens Somatom Balance spiral scanner®) of the thorax was obtained using 5mm cuts after administration of 100ml of intravenous contrast with a 30s delay. Scans were deemed conclusively negative if there was no mediastinal haematoma, no mediastinal air, and the missile track was not in close proximity to vital structures. Alternatively, CT scans were deemed inconclusive if they contained a mediastinal haematoma, pneumomediastinum, or demonstrated proximity of missile track to mediastinal structures (Fig. 1). Those with an inconclusive CT scan proceeded to angiography and/or barium swallow and/or cardiac ultrasound. Patients with conclusively negative CT scans, and/or normal angiograms, oesophograms and cardiac ultrasound were monitored in a high care unit for 24h.

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Figure 1. CT scan of thorax. (A and B) Conclusively negative CT scan (bullet tract away from vital structures). (C and D) Inconclusive CT scan. *Grey arrows indicates bullet tract in A–D. *Dashed white arrow in C and D shows pneumomediastinum and mediastinal haematoma, respectively.

Results 

Sixty-two patients with TMGSWs, of whom 50 were haemodynamically stable, were identified There were 48 (98%) men with a mean age of 28 (range 16–52) years. The mean triage revised trauma score (RTS) on admission was 11 (range 10.5–11). A chest radiograph was obtained in all patients and tube thoracostomy inserted as required. Before the introduction of CT scanning into the protocol, angiography, barium swallow and ultrasound were the most common first line investigations performed and were done in 15 non-consecutive patients; results of which were normal. A total of 35 CT scans were performed, of which 29 (82.9%) were considered conclusively negative, and no further diagnostic tests performed. The remaining six patients with inconclusive CT scans proceeded to angiography and barium swallow, the results of which were also normal. Thoracic injuries included: 37 patients (74%) with either unilateral or bilateral pneumothoraces, haemothoraces or haemo-pneumothoraces, 38 (76%) with lung contusion, 18 (36%) with complete thoracic spinal cord paraplegia, and 16 (32%) with rib fractures. Complications and their management are shown in Table 1. Table 2 summarizes the current costs of the various investigations performed and the 72% cost-saving gained when CT is employed as a screening tool. There were no missed injuries and no mortality.

Table 1. Complications and management

	Complication	N	Management
	Thoracic
	Pneumonia	3	Antibiotics
	ARDS	2	Supportive-ventilation treatment
	Atelectasis	2	Physiotherapy
	Empyaema	1	Tube thoracostomy
	Chest wall sepsis	3	Incision, drainage and debridement
	Extrathoracic
	Deep vein thrombosis	1	Anticoagulation
	Sacral bedsore	1	Debridement and flap

ARDS: acute respiratory distress syndrome.

Table 2. Cost analysis

	Investigation	Cost (ZAR)
	Oesophography	163
	Ultrasound	144
	Angiography	7112
	Total	7419
	Helical CT scan with intravenous contrast (chest)	2016
	Savings	5403 (72%)

ZAR: South African rand.

Discussion 

Evaluation of patients with TMGSWs remains a challenge to the trauma surgeon. Haemodynamically unstable patients generally have potentially lethal cardiac or vascular injuries and require immediate surgery.1, 2, 6, 8 Haemodynamic stable patients can be uninjured, or have occult vascular, oesophageal and cardiac injuries. Therefore, aggressive diagnostic work-up of these patients is advocated in order to avoid missed injuries with disastrous consequences. Patients who are haemodynamically stable can safely undergo diagnostic evaluation before any surgical intervention. In our unit, diagnostic workup has traditionally included angiography; oesophagraphy and cardiac ultrasound. Pericardial window and bronchoscopy is reserved for equivocal cardiac ultrasound examinations and tracheobronchial injuries with massive air leaks causing ventilatory compromise, respectively. The use of CT scan, as a non-invasive diagnostic modality, in penetrating trauma has greatly increased. Chest CT scans findings of a mediastinal haematoma, peumomediastinum or missile track proximity to major mediastinal structures have been shown to be correlated with potential mediastinal injury. Nicole et al., in a 2-year retrospective study of 22 stable patients with transmediastinal gunshot wounds demonstrated the efficiency of contrast enhanced helical CT scans for evaluating potential mediastinal injuries.7 Fifteen patients in their series had a negative scan, were followed clinically in a monitored setting with no missed injuries. Four of the patients with positive scans required only one secondary study (angiography or oesophography) to complete their diagnostic evaluation. These studies were normal. Similarly, Hanpeter et al., in a prospective study of 24 patients showed CT scan to be reliable in evaluating the trajectory of transmediastinal gunshot wounds and demonstrated the potential clinical utility of CT scan in influencing further clinical decisions.4 One patient in their series required sternotomy for removal of a bullet embedded in the myocardium solely on the basis of the results of the CT scan. Because of proximity of the bullet track, 12 patients required further evaluation with eight angiograms and nine oesophageal studies. One of these patients had a positive angiogram (bullet resting against the ascending aorta), and underwent sternotomy for removal; all the other studies were normal. The remaining 11 patients were found to have well-defined tracks that approached neither the aorta nor the oesophagus, and no further evaluation was done. There were no missed injuries in the latter group. In these two studies and the current series, the sample of patients with significant injuries is small and therefore lacks power. Additional studies are therefore required to verify the positive predictive value of CT scanning. In 82.9% of our patients, CT scanning clearly demonstrated the missile track to be away from mediastinal structures, thus eliminating the need for any further diagnostic intervention. These patients were safely observed without any missed injuries. The remaining six patients with inconclusive CT scans underwent further diagnostic evaluation. The combined contrast load of CT scan and angiography leading to contrast-induced nephropathy did not occur in any of the patients. A cost analysis showed that the reduced need for further investigations after a conclusively negative CT scan translates to a cost saving of approximately Rs. 5000.00, a 72% decrease in charges.

Conclusion 

Contrast-enhanced helical CT scanning is a safe, efficient and cost-effective diagnostic tool for evaluating haemodynamically stable patients with TMGSWs. Our current instuition algorithm is presented in Fig. 2.

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Figure 2. Management algorithm for patients with transmediastinal gunshot wounds.