Fine‑needle aspiration cytology of isolated skull nodule: Unfolding the clinical spectrum.

ABSTRACT

Follicular thyroid carcinoma (FTC) has been classified as either minimally invasive or widely invasive carcinoma and shows a propensity for blood‑borne metastasis. Most common sites of metastasis are lung and bone followed by brain, liver, and skin. Minimally invasive FTC (MIFTC) is characterized by limited capsular and/or vascular invasion with good long‑term outcomes, some cases of which show a poor prognosis because of severe distant metastasis. Skull metastasis in adults commonly arises from the lung, breast, and prostate and uncommonly from the thyroid. In our case, fine‑needle aspiration cytology of isolated skull nodule was a reliable tool in the diagnosis of metastasis and suggesting the primary in thyroid thereby prompting early workup of a patient. The case is unique since it represents the rare disseminated metastasis from MIFTC with incomplete capsular penetration alone without angioinvasion that can behave as aggressively as a widely invasive FTC.