Cytologic diagnosis of a solitary brain metastasis from papillary carcinoma of the thyroid. A case report.

BACKGROUND: Papillary carcinoma of the thyroid metastasizes to the brain in rare instances. In published series and case reports of metastatic papillary thyroid carcinoma, diagnosis of central nervous system (CNS) metastases has been determined by histologic methods. We present a case of papillary carcinoma metastatic to brain diagnosed by cytologic methods. CASE: A 43-year-old female, initially diagnosed at age 12 with papillary carcinoma of the thyroid metastatic to regional lymph nodes and lung, presented with head aches of increasing frequency and severity. A computed tomography scan confirmed a 1-cm nodule in the right inferior frontal lobe of the brain. For clinical reasons, the patient was followed with serial imaging for five years. At age 48 there was significant progression of the CNS disease, and the patient underwent stereotactic biopsy with drainage of cyst fluid. Cytologic examination of the cyst fluid and immunocytochemical studies confirmed the typical features of papillary thyroid carcinoma, including papillary clusters of cells with finely granular chromatin, micronucleoli, nuclear grooves and an associated psammoma body. CONCLUSION: Neurocytology is a useful technique in the examination of cystic lesions of the brain and may be the sole technique for determination of diagnosis.