3. Subtypes of craniopharyngioma

Craniopharyngiomas are benign lesions which arise from the neuroepithelium in the sellar region. They are classically subdivided into two distinct entities based on both genetic and morphologic differences. Adamantinomatous CP (aCP), primarily seen in childhood, occurs more commonly than papillary CP (pCP), which is more often seen in adults [2]. In histologic sections, adamantinomatous CP is poorly circumscribed, often multi-cystic and calcified, and is associated with β-catenin and epidermal growth factor receptor (EGFR) overexpression. Papillary CP, on the other hand, is well-circumscribed, less calcified, characterized by solid components, and displays less adherence to surrounding structures [2]. Furthermore, pCP is made up of fibrovascular stroma lined by well-differentiated squamous epithelium [2, 3].

In terms of histologic appearance, aCP usually shows nests and trabeculae of epithelium in fibrocollagenous stroma, with peripheral cells showing nuclear palisading, loose central cells termed "stellate reticulum," and abundant keratin, cholesterol crystals, necrosis, and inflammation. Papillary CP is well circumscribed, composed of the cores of fibrovascular stroma lined by well-differentiated squamous epithelium that may separate to form pseudopapillae which resembles squamous papilloma and without xanthogranulomatous inflammation. In molecular staining of these tumors, the lack of expression of CK8 and CK20 keratin suggests a craniopharyngioma, which differentiates them from Rathke's cleft cyst or pituitary pars intermedia. More recently, VE1 staining has also been utilized to identify BRAF mutations which can help to differentiate between Rathke's cleft cyst and craniopharyngioma [4].
