Dysplastic Megakaryocytes in a Gallbladder Neck Lymph Node in a Patient With Essential Thrombocythemia: A Case Report.

A woman in her 60s with a known history of JAK2-positive essential thrombocythemia presented with a one-week history of jaundice. Laboratory testing revealed elevated bilirubin and alkaline phosphatase levels. Abdominal ultrasonography identified a 1-cm gallstone, and laparoscopic cholecystectomy was performed. Histopathological evaluation revealed chronic cholecystitis along with a 5-mm lymph node in the gallbladder neck harboring atypical megakaryocytes with multinucleation and nuclear lobulation. Immunohistochemistry confirmed megakaryocytic origin with strong positivity for CD61 and supportive positivity for Factor VIII, while epithelial and lymphoid markers were negative, ruling out metastatic carcinoma or lymphoma. This case underscores the rare involvement of lymph nodes by dysplastic megakaryocytes in essential thrombocythemia and highlights the importance of considering hematologic malignancies in the differential diagnosis of lymphadenopathy.