Case Report: Mature cystic teratoma of the diaphragm in an adult male: a rare case and literature review.

Background: Teratomas are germ cell tumors that most commonly arise in the ovaries and testes, whereas the diaphragm is an exceptionally uncommon site of origin. To date, very few cases of diaphragmatic teratomas have been reported worldwide. The rarity and non-specific clinical presentation of these tumors often pose significant diagnostic and reconstructive challenges. Case presentation: A 34-year-old man presented with mild subxiphoid traction discomfort. Laboratory tests revealed an isolated elevation of serum carbohydrate antigen 19-9 (CA19-9) at 401.00 U/mL. Contrast-enhanced computed tomography demonstrated a 5.1 × 4.5 cm mixed cystic-solid mass on the left hemidiaphragm. The patient successfully underwent laparoscopic complete excision of the mass. Because the extensive dissection inherently destroyed the left crus and enlarged the esophageal hiatus, a primary crural repair with concurrent prophylactic Nissen fundoplication was performed to prevent iatrogenic hernia and refractory reflux. Histopathological examination confirmed a mature cystic teratoma of the diaphragm. At the 3-month follow-up, the patient remained completely asymptomatic, without dysphagia or reflux, and demonstrated normalized CA19-9 levels with no radiologic evidence of recurrence. Conclusions: Isolated CA19-9 elevation may be associated with rare primary diaphragmatic teratomas. Furthermore, concurrent laparoscopic hiatal reconstruction (e.g., Nissen fundoplication) provides an excellent, structurally sound functional cure for large tumors intimately adhering to the diaphragmatic crus.