Page 405 - Small Animal Internal Medicine, 6th Edition

CHAPTER 24 Disorders of the Pleural Cavity and Mediastinum 377

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FIG 24.4
Blebs can be seen in this intraoperative image of the lung
of a dog that presented with spontaneous pneumothorax.
The size of these blebs precluded their identification by
thoracic radiography or computed tomography. (Courtesy
Dr. Guillaume Pierre Chanoit.)

Pleurodesis is used in the management of people with
recurrent pneumothorax. Thus far, a consistently successful
technique has not been found for obliterating the pleural
space in dogs or cats. The infusion of autologous blood into
the pleural cavity has shown some promise in dogs, perhaps
functioning as a “patch” over an ongoing leak rather than
obliterating the pleural space. Case reports are limited, and FIG 24.5
dogs with ongoing leakage from traumatic pneumothorax Ventrodorsal view of the thorax of a cat with an anterior
seemed most responsive (Oppenheimer et al., 2014). mediastinal mass. Soft tissue opacity fills the anterior
Regardless of the treatment used, recurrence is a possibil- mediastinum and obscures the border of the heart.
ity. Accurate diagnosis of the underlying lung disease and
determination of the extent of involvement through a thora-
cotomy assist in determining the prognosis. fluid is present. Pleural fluid can both mimic the appearance
of a mass and obscure its borders. Ultrasonography done
before removal of the pleural fluid is helpful in identifying a
MEDIASTINAL MASSES mass and determining the extent to which surrounding
structures are involved.
Mediastinal masses can cause inspiratory distress as a result Thoracocentesis and fluid analysis should be performed
of displacement of lung tissue by the mass itself or by the in animals with pleural effusion. Lymphoma can frequently
secondary pleural effusion that may develop. Additional be diagnosed through identification of malignant cells in the
clinical signs such as coughing, regurgitation, and facial effusion. Transthoracic fine-needle aspiration or biopsy can
edema may be present. Neoplasia is the primary differential be performed to obtain specimens for microscopic evalua-
diagnosis. Lymphoma involving the mediastinum is tion of the mass itself. Aspiration cytology is generally per-
common, particularly in cats. Other types of neoplasms formed initially, followed by biopsy if a cytologic diagnosis
include thymoma and rarely thyroid carcinoma, parathyroid is not obtained. Transthoracic biopsy specimens can often be
carcinoma, and chemodectoma. Nonneoplastic mass lesions obtained relatively safely with ultrasound guidance, particu-
such as abscesses, granulomas, hematomas, and cysts are larly if the lesion is solid rather than cystic. A study by Lana
other possibilities. et al. (2006) demonstrated the usefulness of flow cytometry
Mediastinal masses in cats can sometimes be palpated of mediastinal mass aspirates in differentiating lymphoma
during gentle compression of the anterior thorax. Radio- from thymoma in dogs.
graphically, mediastinal masses appear as soft tissue opaci- Surgical exploration or thoracoscopy may be necessary
ties in the anterior mediastinum (Fig. 24.5). However, it can for biopsy of small lesions, cavitary lesions, and lesions adja-
be difficult to accurately identify a mediastinal mass if pleural cent to the heart or main blood vessels. Complete excision