Giant Pleomorphic Adenoma of the Lacrimal Sac Initially Suspected to Represent a Sinonasal Malignancy 16 Years After Dacryocystorhinostomy

Background and Clinical Significance: Tumors of the lacrimal drainage system are rare but clinically important diagnostic pitfalls because they may mimic benign lacrimal drainage obstruction, chronic dacryocystitis, or sinonasal disease. Pleomorphic adenoma (PA) in this region is exceptionally rare, and delayed recognition may allow progressive extension into adjacent structures. Case Presentation: A 51-year-old woman presented with left nasal obstruction 16 years after external dacryocystorhinostomy for presumed lacrimal drainage obstruction. Examination showed a firm left lacrimal sac mass, proptosis, mild ocular motility limitation, and an intranasal mass. Computed tomography and magnetic resonance imaging showed a large lesion centered in the lacrimal sac region and extending into the nasolacrimal duct, nasal cavity, and maxillary sinus, with orbital displacement. Preoperative biopsy showed epithelial neoplastic tissue without definitive malignant features, but low-grade epithelial malignancy could not be excluded. Complete en bloc excision and medial/inferior orbital wall reconstruction with an autologous calvarial outer table bone graft were performed. The tumor measured 55 × 35 × 25 mm. Final histopathology confirmed PA without malignant transformation. At 2 years postoperatively, there was no recurrence, and proptosis and ocular motility limitation had improved. Conclusions: This case illustrates two diagnostic pitfalls: an underlying tumor may masquerade as lacrimal drainage obstruction, whereas a large benign PA may clinically and radiologically mimic malignancy. Long-standing or atypical unilateral lacrimal symptoms should prompt consideration of tumors and selected use of imaging and tissue diagnosis before lacrimal drainage surgery.