Ectopic hamartomatous thymoma (EHT) or branchial anlage mixed tumour is a rare benign tumour of the lower neck showing an admixture of spindle cells, epithelial islands, and adipose cells. The exact tumour derivation is uncertain, but an origin from the branchial arch, a remnant of primitive ectoderm from the cervical sinus of His, is postulated. The differential diagnoses of EHT include benign and malignant tumours with a biphasic pattern. One entity with a close morphological similarity is lipomatous pleomorphic adenoma or pleomorphic adenoma with lipomatous differentiation.
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