Reeve, M.

Abstract Introduction Mediastinal masses may exhibit various clinical and pathological features. Posterior mediastinal lesions are often neurogenic, followed by lymphadenopathy, extramedullary hematopoiesis, paraspinal abscess, and rarely, foregut duplication cysts (prevalence: 0.122%). Given the rarity and diagnostic challenges, these masses are often biopsied, though may not be ideal. We present a case of esophageal duplication cyst (EDC). Case presentation A 33-year-old woman with mild intermittent asthma, had initially presented to an outside facility for chronic productive cough, episodic chest tightness and dyspnea both at rest and with exertion, inspiratory and expiratory wheezes. Despite multiple courses of prednisone for presumed asthma exacerbation, her symptoms persisted. An initial Computer Tomography (CT) Chest demonstrated a 5 x 4 x 3 cm mass within the visceral mediastinum. Bronchoscopy with endobronchial ultrasound and transbronchial needle aspiration of the mediastinal lymph nodes was nondiagnostic, showing scant lymphocytes and abundant mucin. Broad autoimmune, connective tissue disease, and infectious disease workups were negative, prompting referral to our facility. Physical exam and labs were unremarkable and pulmonary function testing showed no evidence of small airway obstruction. A High-Resolution CT Chest revealed a 3.1 x 3.7 x 4.5 cm noncalcified, well-circumscribed mass soft tissue density, adjacent to the esophagus with elevated Hounsfield units close to esophagus. Ultimately duplication cyst was suspected and Magnetic Resonance Imaging (MRI) with contrast showed high T1 and T2 signal within the lesion and no enhancement after contrast, deemed compatible with proteinaceous/hemorrhagic cyst (Figure 1 A-D). Biopsy was deferred given diagnostic MRI characteristics, and risk of secondary infection. The diagnosis of EDC was confirmed via multidisciplinary thoracic tumor board revision. Ultimately, she was referred for surgical resection. Discussion The incidence of EDC is 1 in 8,200, with a two-fold male prevalence over women. These patients may present with dysphagia, cough, stridor, pain, or arrhythmia since childhood, or may be entirely asymptomatic. EDCs can develop along the esophagus, with 90% lacking communication with the esophageal lumen. Although posterior mediastinal mass typically require biopsy to exclude malignancy, tissue biopsy should be avoided in cases with suspected duplication cyst given risk of infection, abscess formation and mediastinitis. Transesophageal endoscopic ultrasonography could further characterize the cyst, however MRI is considered the gold standard diagnostic modality. Conclusion MRI is the gold standard diagnostic modality of EDC. Biopsy should be avoided given the risk of infection. Clinicians should consider a broad differential for posterior mediastinal mass and avoid unnecessary invasive testing.