Isolated Intracranial Extramedullary Hematopoiesis in an Adult Patient

This article describes the case of a 56-year-old male patient who presented with a headache and swelling on the left side of his head. Medical examinations, including non-contrast computed tomography (CT) and contrast-enhanced magnetic resonance imaging (MRI), revealed the presence of an expansile soft tissue lesion in the frontoparietal bone structures, causing compression of the brain tissue. Further immunohistochemical analysis confirmed the diagnosis of extramedullary hematopoiesis (EMH) in the bone lesion, with predominant involvement of the myeloid series. EMH is a compensatory mechanism of the body to meet the demand for erythropoiesis. While EMH is commonly associated with thalassemia in children and myelofibrosis in adults, it can occur in various tissues throughout the body, including the intracranial region, although it is rare. The imaging findings of EMH on MRI typically show iso-hypointense signals on T1-weighted images and hypointense signals on T2-weighted images due to the presence of hemosiderin. However, in this case, the lesions appeared hyperintense on T2-weighted images, which posed a challenge in the differential diagnosis. The article highlights the importance of clinical evaluation and imaging findings in diagnosing EMH, as these lesions can resemble other conditions such as metastases, angiomatous meningioma, chloroma, or epidural hematoma. Teaching Point: Isolated cases of intracranial EMH should be considered as a differential diagnosis in adult patients as they may be radiologically confused with malignant conditions such as metastases, angiomatous meningioma, chloroma or epidural hematoma.