Incremental role of Nuclear techniques in diagnosis and management of Type 3 Sternal wound dehiscence after median sternotomy

Introduction: Median Sternotomy is the choice of access for most major cardiac surgeries. An uncommon complication of this access route is sternal infection and sternotomy wound dehiscence. Redo and emergency operations are the most important risk factors. Early identification and thorough debridement of infected and devitalised tissue is essential to decrease this arduous morbidity and the costs of prolonged treatment.

Objectives: To study the role of Tc MDP bone scan and Gallium 67 citrate infection imaging to determine the site of occult infection, and determine the extent of sinus tracts in patients with type 3 sternal dehiscence wounds (as per Pairolero and Arnold's classification).

Methods: Retrospective study of 52 patients with sternotomy wound dehiscence was conducted in our institute between January 2014 - Dec 2015. Antibiotics, debridement, negative suction wound therapy and closure either primary or with flap cover was offered after achieving a healthy wound environment. 5 / 52 patients with non healing chest infection underwent bone scan with gallium scan. Gallium SPECT CT was obtained in all. All patients underwent further debridements as guided by the imaging reports and after achieving good wound control underwent flap cover for wound closure.

Results: Gallium and Bone scans when combined with SPECT CT gave following results in the 5 patients. Patient 1 - Low probability of osteomyelitis of sternum. Substernal soft tissue focal increased gallium uptake at the level of 2nd rib. Patient 2 - Chronic active soft tissue infection in left anterior chest wall adjacent to the lower part of body of sternum, tracking down bilaterally into anterior chest wall and abdominal wall upto level of 12th rib on left side and 10th rib on right side. Patient 3 - Active chronic osteomyelitis of sternum with surrounding soft tissue inflammation extending to subcutaneous planes of lower anterior ribs bilaterally. Patient 4 - Active infection in sternal region, extending into the left 7th and 8th sternocostal region and medial end of left 8th rib. Patient 5 - Active infection involving sternum and lower anterior costochondral junctions and 5th ribs bilaterally. Nuclear imaging identified active infection at sites distant from the sternum along with associated findings of sternal osteomyelitis.

Results: Sternal wound dehiscence after median sternotomy is an uncommon complication but one with a high morbidity and mortality rate. Pairolero and Arnold have classified them into 3 types Type 1 – Initial presentation with serosanguineous drainage. Cellulitis absent and mediastinum is soft and pliable. Osteomyelitis and costochondritis are absent and cultures are usually negative. Type 2 - Occurs within first few weeks as purulent drainage. Cellulitis is present with mediastinal suppuration. Osteomyelitis is frequent although costochondritis is rare. Cultures are invariably positive. Type 3 – Occurs later with chronic draining sinus/es. Cellulitis is localized and mediastinitis is rare. Osteomyelitis, costochondritis or a retained foreign body always present. Cultures are positive. Of 52 patients with sternotomy dehiscence, 5 patients of type 3 sternal wound dehiscence whose true extent of infected tissue could not be assessed was helped by three phase Bone and Gallium imaging. Additional infective foci were present in the sternum as well as away from the sternum in these cases.

Conclusion: Tc MDP Skeletal scintigraphy and Gallium 67 citrate imaging in combination with SPECT CT has an incremental role in accurate identification and providing a road map to the sites of occult infection in sternotomy patients. The culprit areas of occult infection were usually located in substernal mediastinum, ribs, costal cartilages and soft tissues of the anterior chest wall.