Nonsurgical resolution of caudal mediastinal paraesophageal abscess in a cat.

A one-year-old, castrated male domestic short hair cat was admitted with a history of anorexia, regurgitation and pyrexia for two days. Fever and leukocytosis were identified. There were a large soft tissue density oval mass in the caudal mediastinum on thoracic radiographs, a fluid-filled oval mass in the caudal mediastinum on ultrasonography, and left-sided and ventrally displaced and compressed esophagus on esophagram. On esophageal endoscopy, there were no esophageal abnormalities. CT findings with a fluid filled mass with rim enhancement indicated a caudal mediastinal paraesophageal abscess. The patient was treated with oral antibiotics, because the owner declined percutaneous drainage and surgery. The patient was admitted on emergency with severe respiratory distress; and ruptured abscess and deteriorated pleuropneumonia were suspected. With intensive hospitalization care and additional antibiotic therapy, the patient had full recovery.

Caudal mediastinal paraesophageal abscess (CMPA) is an uncommon mediastinal disease in dogs and cats, demonstrating abscess formation outside the esophagus in the caudal mediastinum. CMPA needs nearly always surgical intervention [4]. We report nonsurgical resolution of caudal mediastinal paraesophageal abscess with antibiotics and supportive care in a cat.

A one-year-old, castrated male domestic short hair cat, weighing 5.4 kg, was admitted with a history of anorexia, regurgitation and pyrexia for two days and decreased appetite, weight loss and nausea for a month. On physical examination, the patient had a fever of 40.4°C and tachypnea. Hematological examination revealed leukocytosis (24,400/µl).

Plain thoracic radiographs showed a large soft tissue density round mass in the caudal mediastinum, multifocal patchy alveolar infiltration in lung field and left caudal pleural thickening (Fig. 1). Abdominal ultrasound revealed a fluid-filled round mass without remarkable blood signals in the caudal mediastinum (Fig. 2). On esophagram using barium sulfate, the esophagus was left sided displaced and compressed by this round mass (Fig. 3). On esophageal endoscopy, there were no esophageal abnormalities including remnant foreign body, inflammation, perforation or fistula. To further evaluate the nature of this round mass, CT was performed under general anesthesia. There was a fluid density round mass with rim enhancement in the caudal mediastinal paraesophageal region. This mass compressed esophagus. And, multifocal patchy infiltration in bilateral lung lobes, severer in the left caudal lung lobe and irregular left caudal pleural thickening were identified (Fig. 4). Therefore, based on these imaging findings, CMPA and pleuropneumonia were diagnosed clinically, although histopathologic and bacteriologic examinations were not performed. The patient was treated with oral antibiotics using amoxicillin and clavulanic acid 62.5mg/cat PO twice daily for 3 days before surgery. The patient showed better clinical signs with antibiotics, and the owner declined percutaneous drainage and surgery on the day of surgery. On 12 days of antibiotics treatment, the patient was admitted to the emergency department with acute respiratory distress. The patient showed tachypnea on physical examination. Body temperature was 39.3°C. Plain thoracic radiographs showed disappearance of the caudal mediastinal paraesophageal mass and increased patchy alveolar infiltration and pleural thickening in the left caudal lung lobe (Fig. 5). The mass was also not identified on ultrasonography. Unfortunately, bacteriologic examination was not performed, because there was only a small amount of pleural effusion, not enough for thoracentesis, in the left caudal lung field. Rupture or leakage of abscess and deteriorated pleuropneumonia were suspected, because there was no remarkable change of CMPA and pleuropneumonia on thoracic radiographs three days ago. On hematology, there was elevated WBC (25,600/µl) including remarkable increases in band neutrophil cells and toxic change in neutrophils. Other clinical chemistry results were within normal limits. The patient was further treated with combination antibiotics using metronidazole 15 mg/kg PO twice daily and amoxicillin and clavulanic acid 62.5 mg/cat PO twice daily with aggressive hospitalization care. The patient had full recovery for 21 days and showed no recurrence of abscess or pleuropneumonia. The patient is doing well without any other complications for one year.

Fig.1.

Right lateral (A) and ventrodorsal (B) thoracic plain radiographs show a soft tissue density round mass located in the caudal mediastinum. Sternal lymph node swelling, focal patchy alveolar infiltration and irregular left caudal pleural thickening are identified.

Fig. 2.

Abdominal ultrasound demonstrates a hypoechoic cavitary oval mass filled with swirling fluid.

Fig. 3.

Esophagram (A; right lateral view, B; ventrodorsal view) demonstrates that the esophagus is displaced to the left and ventrally and narrowed by the caudal mediastinal paraesophageal mass.

Fig. 4.

Computed tomography indicates a hypoattenuating abscess with rim enhancement in the caudal mediastinum (asterisks in A, B, C, D and F). The esophagus (arrows in A, C, D and F) was compressed and displaced to the left by adjacent CMPA. There are no evidences to support association between the esophagus and CMPA at this time. There are multifocal patchy infiltration in bilateral lung lobes (arrowheads in C and E) and left caudal pleural thickening (black arrows in E).

Fig. 5.

Right lateral (A) and ventrodorsal (B) thoracic radiographs show resolution of CMPA and deterioration with left caudal pleuropneumonia when the patient is admitted on emergency with acute respiratory distress.

CMPA is an uncommon disease characterized by abscess formation adjacent to the esophagus within caudal mediastinum [4]. General clinical signs of CMPA are pyrexia, lethargy and regurgitation associated with abscess and paraesophageal mass effect. Additionally, in the case of concurrent pulmonary infiltration or pleural effusion, there is coughing or respiratory distress [3, 4, 6, 8, 9, 13]. Main causes of CMPA are known for esophageal disorders including perforation due to an esophageal foreign body, endoscopic trauma and inadequate wound closure or surgical materials left within the operative field in case of esophageal cancer surgery in human and veterinary medicine [1, 3,4,5,6,7,8, 10, 11, 13]. This patient had CMPA and pleuropneumonia concurrently, although the etiology is poorly understood. There were no evidences associated with esophageal abnormalities. The esophagus was only associated with clinical signs of vomiting and anorexia, because of extrinsic compression by CMPA.

The most common bacteria associated with CMPA are Nocardia sp and Actinomyces sp in the previous veterinary studies [4, 13]. However, most reposts submit no results of bacteriology, because of previous antibiotics treatment [4]. Unfortunately, sampling from CMPA was not performed, because the owners were afraid of complications of percutaneous drainage.

Treatment of CMPA needs mediastinal drainage with antibiotics effective against anaerobic bacteria. CMPA has favorable prognosis after aggressive surgical drainage. As initial CMPA drainage method, there has been surgical mediastinotomy and transdiaphragmatic abscess omentalization [4, 6]. In human, percutaneous drainage is indicated, if the patients are old and have disseminated intravascular coagulation, immunodeficiency, malnutrition or high risk of re-operation [2, 12]. Successful management of CMPA may depend on early diagnosis followed by aggressive surgical drainage and suitable antibiotic therapy, and correction of the underlying predisposing conditions. Fortunately, without surgical drainage, this patient had good prognosis, because of early diagnosis of CMPA, spontaneous rupture of mediastinal abscess, suitable antibiotic therapy and intensive supportive care.

Diagnostic imaging modalities, such as thoracic radiographs, abdominal ultrasonography, esophagram, endoscopy and CT, were all helpful to evaluate CMPA in this patient by stages. Plain thoracic radiographs are usually the first choice exploration in CMPA and offer rapid information of the lung and mediastinum including the esophagus. This cat had remarkable round widening of caudal mediastinum and suspicious pleuropneumonia. However, esophageal abnormalities or association could not be evaluated. This mass showed homogeneous soft tissue density without air on plain radiography. Because of no gas in the mass, abdominal ultrasonography was helpful. On ultrasonography, caudal mediastinal widening was a hypochoic movable fluid-filled mass with well defined wall in the caudal mediastinum. A hypoechoic mass with heterogeneous internal echoes or septation, hyperechoic thick wall and peripheral blood signals can be specific ultrasonographic findings of abscess [9, 10]. Therefore, the ultrasonographic differential diagnosis includes a caudal mediastinal abscess. But, it could not also evaluate for esophageal relations. Esophagram with barium sulfate ruled out esophageal hiatal hernia and showed paraesophageal mass effect; left and ventral displacement of esophagus with flattening of esophageal lumen. There was no leakage of the contrast medium between esophagus and a caudal mediastinal mass. Endoscopy showed no abnormalities in the esophageal mucosa and ruled out remnant esophageal foreign body or small perforation. Therefore, the association and complement between plain thoracic radiographs, ultrasonography, esophagram and endoscopy were necessary for diagnosing CMPA in this patient. However, above all, CT was considered the best imaging modality of CMPA diagnosis compared with the previous imaging procedures. CT was specific in determining the nature of fluid fillled paraesophageal mediastinal mass and pleuropneumonia. A hypoattenuating oval mass with rim enhancement of the circumference can be specific images of abscess on CT [4, 10, 14]. Therefore, CT findings were conclusive for CMPA in this patient. And, CT could rule out any other concurrent or underlying diseases. And, it helps choosing the precise surgical plan.

This is the first known documentation of non-surgical resolution of CMPA and pleuropneumonia by antibiotics in a cat. This case is unusual, because general CMPA needs surgical or percutaneous drainage, but this patient had suspicious spontaneous rupture of abscess and worse pleuropneumonia and overcame this condition with proper antibiotics and intensive supportive care. CMPA may be expected with good clinical outcome with prompt treatment after an early diagnosis, even failure of bacteriological examination and surgical drainage. However, CMPA may be life-threatening if not recognized in time. Fever and leukocytosis may be the most considerable evidences for abscess. And, readily available diagnostic imaging, such as thoracic radiographs, ultrasonographs, esophagram or endoscopy, is helpful for the diagnosis of CMPA complementally. However, CT is the critical diagnosing modality of CMPA.