RESUMEN
BACKGROUND Chylothorax is a rare condition caused by the leak of chyle into the pleural cavity. Malignancy, especially advanced lymphomas, are the most common non-traumatic causes of chylothorax. When thoracentesis and the following pleural effusion studies reveal the fluid to be a chyle, it is important to look at the patients' history and understand the possible etiological factors, as the appropriate management can differ. In some instances, the true reason behind the chylothorax can be a diagnostic challenge, as presented in this case. CASE REPORT We report a case of a patient in her 70s presenting with progressive dyspnea at rest and non-productive cough. A chest X-ray showed subtotal right pleural effusion that was revealed to be a chylothorax. A CT scan was performed and revealed mediastinal, abdominal, and retroperitoneal lymphadenopathy, that, compared to the CT results 6 years ago, when for the first time enlarged lymph nodes were discovered by thyroid ultrasound, was without any progression. Initial diagnostic tests were inconclusive, and the goal was to rule out other differential diagnoses while maintaining a minimally invasive diagnostic approach. A video-assisted thoracoscopic surgery with mediastinal lymph node dissection and biopsy led to a diagnosis of follicular lymphoma. CONCLUSIONS This clinical case highlights not only an uncommon follicular lymphoma complication but also is an example of a diagnostic challenge due to certain clinical features being misleading from the true cause of the chylothorax. After a wide variety of investigations were applied, the patient was finally diagnosed with non-Hodgkin lymphoma. Successful treatment led to a full metabolic remission.