BRAF V600E mutation is a useful marker for differentiating Rathke’s cleft cyst with squamous metaplasia from papillary craniopharyngioma

Excerpt

Rathke’s cleft cyst (RCC) is a non-neoplastic cyst arising in the sellar region. RCCs are usually small asymptomatic lesions identified at autopsy. However, they can enlarge, causing clinical signs and symptoms as a result [1]. RCCs should be differentiated from various cystic lesions arising in the sellar region, such as craniopharyngiomas (CPs), cystic pituitary adenomas, arachnoid cysts, and dermoid cysts. Of these, it is important to distinguish RCCs from CPs clinically, because the biology and treatments of the two entities differ. However, the relationship between RCCs and CPs is controversial due to the existence of a histological transitional form, the ciliated CP, which has a mixed histology overlapping the features of the two entities [1]. RCCs are usually lined by ciliated cuboidal or columnar epithelium, whereas CPs are characterized by a squamous epithelial lining. Therefore, the diagnosis of RCC based on the clinical, radiological, and pathological characteristics is usually established with little difficulty. However, RCCs can be accompanied by squamous metaplasia (SM) and a pathological distinction between RCC and papillary CP can be difficult when SM is prominent in RCCs or is identified in a limited volume of the specimen. Furthermore, RCCs with SM can overlap the characteristics of ciliated CPs both pathologically and clinically (Fig. 1). Based on these findings, some authors have suggested that RCCs with SM can transform into papillary CPs via ciliated CPs, while others consider all transitional forms to be true RCCs, not a precursor or transitional lesion of papillary CP, because SM occurs frequently in a normal persistent RCC and can arise in both normal and neoplastic adenohypophyseal cells [1]. These arguments might originate from the unknown pathogenesis of papillary CP.

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