Extra‐medullary haematopoiesis: A pictorial review of its typical and atypical locations

Abstract

SummaryExtra-medullary haematopoiesis (EMH) occurs in many haematological disorders and is secondary to insufficient bone marrow function or ineffective erythropoiesis. It usually presents as haematopoietic masses in several typical and atypical body locations. This pictorial review briefly discusses the common EMH locations encountered in clinical practice, including the liver, spleen, lymph nodes and paravertebral regions. Unusual presentation as focal hepatic and splenic masses is also discussed. Some atypical EMH locations are then presented together with their pathophysiology and relevant illustrations. These include EMH in the intra-spinal canal, pre-sacral region, nasopharynx and paranasal sinuses. Intra-spinal EMH can cause cord compression and present with neurological symptoms. In these cases, urgent treatment may be required. Haematopoietic masses in the other atypical locations can present with obstructive symptoms or may be diagnosed incidentally on imaging. EMH in unusual locations need to be monitored with follow-up imaging to ensure their stability. In some circumstances, tissue biopsy is appropriate to confirm the diagnosis and exclude other sinister pathology (e.g. malignancy). Treatment is only required where symptoms are present. Management options include blood transfusion, radiotherapy, hydroxyurea or surgical resection in selected cases.

Extramedullary hematopoiesis: Elucidating the function of the hematopoietic stem cell niche (Review)

“…By week 11, HSCs and the bone marrow niche environment are established in the marrow cavity (30). By contrast, the spleen performs a minor function as a site of erythropoiesis (26). At each stage of development, stromal cell/HSC interactions via cytokines, chemokines and growth factors have significant roles in the maintenance of normal hematopoiesis (31).…”

“…However, this condition has not been identified physiologically in adults. Therefore, the pathophysiological variations in hematopoietic stem cells (HSCs) and their microenvironment may be a component of the homing, proliferation and maturation processes associated with hematopoietic cells in the extramedullary organs of adults; although, there is currently a dearth of studies addressing the prevalence and fundamental processes of EMH (1). This may be explained by the fact that EMH is generally identified as a secondary or accessory event to another disorder, including benign hematologic disorder (2) or cancer (3), in certain cases developing independently or lacking apparent trigger and without clinical or diagnostic implications (4,5).…”

Imaging studies in extramedullary hematopoiesis of the spleen

“…To our knowledge, only a few cases of focal extramedullary hematopoiesis have been reported with imaging descriptions [5]. In fact, spleen tumors are usually detectable but not easily characterizable by imaging due to overlapping patterns between benign and malignant nodules.…”

“…Even if none of the above-described findings is neither sufficient nor necessary for definitive diagnosis, the association of well-defined lesion, highly and inhomogeneously enhancing, with pseudocystic areas, and medium-high signal intensity in MRI-T2 and diffusion weighted-not resembling hemangioma or pseudotumor, could suggest radiologists a diagnosis of intrasplenic extramedullary hemopoiesis [4,5] and then clinicians to perform tests for hematological disorders including myeloproliferative neoplasms, such as bone marrow biopsy, JAK2V617F of MPL mutations in addition to CBC, before referring the patient for splenectomy which can bring some risks of complications.…”

Imaging the posterior mediastinum: a multimodality approach

“…4), or low signal intensity with iron deposition (12,21). Mild homogeneous enhancement on both CT and MRI is usually seen in active lesions, whereas a heterogeneous enhancing pattern is more common in inactive lesions because of iron deposition or fatty replacement (22). In rare cases of extension into the spinal canal, MRI is required for the evaluation of spinal cord compression, which may lead to irreversible neurologic damage if untreated (23).…”