Masquerade syndrome: sebaceous carcinoma presenting as an unknown primary with pagetoid spread to the nasal cavity.

Sebaceous carcinoma of the eyelid is an uncommon tumour with unusual modes of presentation. It can remain occult at the primary site, without producing any mass, masquerading as chronic blepharoconjunctivitis, while setting up metastases in the regional lymph nodes especially in the pre-auricular group. We report here a case that not only masqueraded as chronic blepharoconjunctivitis with nodal metastases from an 'unknown primary' in the neck, but whose tumour spread in a pagetoid manner along the nasolacrimal duct producing a nasal tumour that was believed to be the 'unknown primary'. This case emphasizes the need for ophthalmologists, ENT surgeons and pathologists to keep sebaceous carcinoma in mind while evaluating patients with chronic blepharoconjunctivitis and cervical node metastases from 'unknown primary'. Histological clues for picking up a sebaceous carcinoma at a metastatic site include a tumour with comedo or ductal growth pattern and intracytoplasmic lipid. [ABSTRACT FROM AUTHOR]