Surgical Pathology Criteria–

Ectopic Hamartomatous Thymoma

Differential Diagnosis

Ectopic Hamartomatous Thymoma bears no resemblance to any type of thymoma

Spindle Cell Lipoma Ectopic Hamartomatous Thymoma
Lacks epitihelioid nests Has epithelioid nests
Has ropy collagen Lacks ropy collagen
Keratin, p63 and smooth muscle actin negative Keratin, p63 and smooth muscle actin positive
Both contain spindle cell and adipose components and both are CD34 positive in the spindled component

 

Extragonadal Teratoma Ectopic Hamartomatous Thymoma
In the neck, most are associated with the thyroid or ectopic thymus Located in subcutaneous fat
May have a variety of differentiated tissues present Restricted to spindled cells with squamous or glandular epithelium and fat
A variety of differentiated epithelial patterns may be present Epithelium in nests or anastomosing cords
Spindle cell component may have a variety of phenotypes Spindle cell component has a myoepithelial phenotype

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