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640 Mediastinal Disease

Patients requiring treatment with the drugs not appropriate and may be life-threatening SUGGESTED READING
listed above may need to receive a decreased in dogs with the MDR1 mutation. Mealey KL: Adverse drug reactions in herding-breed
VetBooks.ir determine appropriate dosage adjustments have Client Education AUTHOR: Katrina L. Mealey, DVM, PhD, DACVCP,
drug dosage or an alternative drug. Studies to
dogs: the role of P-glycoprotein. Compend Contin
Educ Vet 28:23-33, 2006.
Owners should be aware of drug sensitivities
not yet been conducted.
Technician Tips if the dog has the MDR1 mutation. Breeders DACVIM
should consider the MDR1 mutation as part
Attempts to save costs by off-label use of of a comprehensive genetic assessment of their EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
large animal ivermectin products in dogs is breeding program.

Mediastinal Disease Client Education
Sheet

BASIC INFORMATION regurgitation, cough, dyspnea, facial/neck/ • Extension from surrounding tissues, com-
forelimb swelling or edema, dysphonia if monly esophagus but also cervical tissues,
Definition recurrent laryngeal nerve involvement trachea, pleural space
Disorders of the mediastinum (potential space • Mediastinal hemorrhage: lethargy, weakness, ○ Esophageal foreign bodies
between the right and left lungs) tachypnea ○ Rupture from esophagitis (after general
anesthesia) or esophageal tear after
Epidemiology PHYSICAL EXAM FINDINGS stricture dilation
SPECIES, AGE, SEX Pneumomediastinum: • Acute: Staphylococcus spp, Streptococcus spp,
• Mediastinal lymphoma: young cats are • Exam may be normal Escherichia coli, Corynebacterium spp
overrepresented. • Subcutaneous emphysema • Chronic: bacterial (Nocardia, Actinomyces,
• Other mediastinal masses more commonly • Respiratory signs if severe: dyspnea, muffled Staphylococcus spp) and fungal (histoplasmo-
affect middle-aged or older animals. breath sounds, hyperresonant thoracic sis, blastomycosis, cryptococcosis) infection
percussion (pneumothorax) reported
GENETICS, BREED PREDISPOSITION • Jugular venous distention • Spirocercosis (dogs)
Mediastinal lymphoma: Asian-breed cats • Shock • Clinical signs due to sepsis, pleural effusion,
Mediastinitis: and compression of vascular or respiratory
RISK FACTORS • Fever structures
• Mediastinal lymphoma: feline leukemia virus • Dyspnea, tachypnea, cough Mediastinal masses:
infection (FeLV [p. 329]) • Edema (head, neck, forelimbs) secondary to • Lymphoma, thymoma, thyroid neoplasia,
• Pneumomediastinum: tracheal laceration/ cranial vena cava syndrome (p. 221) chemodectoma, thymic cysts, granulomas
avulsion • Dysphagia, regurgitation • Clinical signs reflect compression of
• Mediastinitis: esophageal foreign body or • Thoracic pain respiratory, cardiovascular, gastrointestinal
rupture • Reduced thoracic compressibility (cats) structures, ± pleural effusion, ± neurologic
• Stridor abnormalities (Horner’s syndrome, laryngeal
CONTAGION AND ZOONOSIS Mediastinal masses: paralysis)
FeLV infection • Reduced thoracic compressibility (cats) • ± Paraneoplastic syndromes: hypercalcemia,
• Cranial vena cava syndrome myasthenia gravis
ASSOCIATED DISORDERS • Respiratory or gastrointestinal signs Mediastinal hemorrhage:
Mediastinal masses: • ± Paraneoplastic signs: weakness, regurgita- • Trauma
• Acquired myasthenia gravis (thymoma) tion, stridor if secondary laryngeal paralysis, • Coagulopathy
• Polyuria and polydipsia (lymphoma) polyuria/polydipsia • Spontaneous thymic hemorrhage
• Horner’s syndrome • Neoplasia
Clinical Presentation • Stridor • Clinical signs related to acute blood loss.
DISEASE FORMS/SUBTYPES Mediastinal hemorrhage:
• Pneumomediastinum • Pale mucous membranes DIAGNOSIS
• Mediastinitis • Tachycardia
• Mediastinal masses • Weakness Diagnostic Overview
• Mediastinal hemorrhage Thoracic radiographs are typically the initial
Etiology and Pathophysiology step in a diagnostic evaluation. If there is a
HISTORY, CHIEF COMPLAINT Pneumomediastinum: mass lesion, advanced imaging such as CT
• Pneumomediastinum: recent trauma, • Penetrating neck wounds is often indicated, but fine-needle aspiration
anesthesia (overinflated endotracheal tube • Tracheal laceration/tear (traumatic; iatrogenic and cytologic analysis or needle, thoracoscopic,
cuff or turning patient without disconnection from endotracheal tubes) or open surgical biopsy and histopathologic
of endotracheal tube), transtracheal wash or • After esophageal surgery (uncommon) analysis of tissue typically is required to establish
jugular venipuncture • Positive-pressure ventilation a definitive diagnosis.
○ ± Subcutaneous emphysema and/or • Secondary to primary pulmonary pathol-
dyspnea ogy Differential Diagnosis
• Mediastinitis (acute): obtundation, inap- Mediastinitis: • Pneumomediastinum: tracheal trauma,
petence, dysphagia, regurgitation • Hematogenous infection pneumothorax
• Mediastinal masses: inappetence, leth- • Penetrating wounds (e.g., bites) and migrat- • Mediastinitis: other causes of sepsis, medi-
argy, polyuria/polydipsia, dysphagia or ing foreign bodies astinal masses/fat/fluid, pleural effusions

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