CHAPTER 69 Thoracoscopically Guided Pulmonary Biopsy
Thoracoscopy can be used to provide a more accurate diagnosis and prognosis in horses with thoracic disease when less invasive diagnostic tools fail to yield an accurate assessment. Common indications for thoracoscopy include (1) exploration of the thorax when neoplasia is suspected or there is pleural effusion of unknown origin, (2) drain placement for relief of pleural effusion or management of abscesses, (3) transection of pleural adhesions, (4) pulmonary biopsy, and (5) window pericardectomy. Thoracoscopy in the standing horse has proven to be safe, well tolerated, and associated with minimal detrimental effects to cardiovascular and pulmonary function of healthy horses and those with chronic lung disease.
Despite the numerous diagnostic modalities available for investigation of equine thoracic diseases, accurate diagnosis and prognostication of some pleuropulmonary diseases often necessitate direct evaluation of pulmonary tissue. Common indications for lung biopsy in horses include suspicion of infiltrative disease, neoplasia, and interstitial disease and for pulmonary research. Transbronchial pinch and percutaneous methods have been used in horses. Recently thoracoscopically guided pulmonary-wedge resection has been described and used in clinical cases and for research purposes.
Thoracoscopically guided lung biopsy has been described as safe and successful in the harvest of tissue samples for histologic and microbiologic examination. Pulmonary tissue samples are collected from the caudodorsal aspect of the lung and, when lung disease is diffuse, tissue at this site appears to be representative of the remainder of the lung. Direct observation of the biopsy site and excellent hemostasis are advantages of this technique that enable surgeons to avoid complications. In addition, the tissue sample obtained is excellent for histologic examination because it contains minimal artifacts and can include both normal and diseased tissue. If a larger tissue sample is desired, multiple wedge resections can be collected. The chief disadvantage of this technique is that tissue access is limited to the periphery of the lung, and samples are useful only for evaluation of peripheral lesions or diffuse interstitial diseases. If pulmonary lesions are seen during thoracoscopy on the broad surface of the lung, a biopsy can be performed with fine-needle aspiration, endoscopic biopsy forceps, or other biopsy instruments.
The instruments used for thoracoscopically guided lung biopsy are the same as those used for laparoscopic surgery and include a 30-degree, 10-mm × 58-cm rigid laparoscope,∗ videocamera,∗ and a 300W xenon light source. Endoscopic forceps† are used to manipulate the lung, and an endoscopic stapler† (EZ endoscopic linear cutter, 45 mm) is used to perform the lung biopsy. The procedure is performed with the horse standing under chemical restraint with xylazine (0.5 to 1.1 mg/kg, intravenous [IV] administration), or detomidine (0.02-0.04 mg/kg, IV), or a continuous IV drip infusion of detomidine (6 μm/kg loading dose followed by an administration rate of 0.8 mcg/kg per minute until the desired effect is observed).