Retroperitoneal chyloma is a rare entity that presents with non-specific symptoms. Although benign, it can cause complications due to the mass effect. In this case report, we present the case of a 24-year-old woman who presented with a complaint of left-sided colicky abdominal pain and mild dysuria for one year. On physical examination, there was only mild abdominal tenderness. Computed tomography (CT) revealed a thick-walled cystic retroperitoneal mass with a small amount of fat in the superior part and a displaced left hydronephrotic kidney. Magnetic resonance imaging (MRI) confirmed the findings and also revealed a fat-fluid level in the cyst. A laparotomy was performed, and the cystic mass, containing milky fluid, was excised. Histopathology showed a pseudocyst with chronic inflammation and a xanthomatous reaction, with no evidence of infection or malignancy. The patient recovered without complications and has not had a recurrence so far. Retroperitoneal chyloma is difficult to diagnose preoperatively. A definitive diagnosis is usually made only after surgery and a histopathological examination. The treatment of choice is a complete excision. Other approaches, such as marsupialization or drainage, will likely result in a recurrence. However, surgery in the retroperitoneal space is associated with a risk of injury to major vessels or organs. In conclusion, retroperitoneal chyloma is a rare entity that is best treated by complete excision. For small lesions, a wait-and-watch approach may be advisable.

BACKGROUND: Chylothorax is a relatively rare but well-known complication of thoracic surgery.
METHODS: A 70-year-old man underwent right upper and middle bilobectomy and systematic lymph node dissection through a posterolateral thoracotomy for lung cancer. On the second postoperative day, he developed chylothorax that was treated with dietary management and pleurodesis. The discharge diminished and his chest tube was removed on the ninth postoperative day. On the 14(th) postoperative day, the patient complained of dyspnea and dysphagia, and imaging studies revealed mediastinal chyloma. Thoracoscopic surgical drainage was performed and the site of chyle leakage was sutured.
CONCLUSIONS: This report presents an unexpected complication of chemical pleurodesis and reviews the indications for surgical intervention in cases of postoperative chylothorax.