Extramedullary hematopoiesis in the absence of myeloproliferative neoplasm: Mayo Clinic case series of 309 patients

Extramedullary hematopoiesis in cancer

Hematopoiesis can occur outside of the bone marrow during inflammatory stress to increase the production of primarily myeloid cells at extramedullary sites; this process is known as extramedullary hematopoiesis (EMH). As observed in a broad range of hematologic and nonhematologic diseases, EMH is now recognized for its important contributions to solid tumor pathology and prognosis. To initiate EMH, hematopoietic stem cells (HSCs) are mobilized from the bone marrow into the circulation and to extramedullary sites such as the spleen and liver. At these sites, HSCs primarily produce a pathological subset of myeloid cells that contributes to tumor pathology. The EMH HSC niche, which is distinct from the bone marrow HSC niche, is beginning to be characterized. The important cytokines that likely contribute to initiating and maintaining the EMH niche are KIT ligands, CXCL12, G-CSF, IL-1 family members, LIF, TNFα, and CXCR2. Further study of the role of EMH may offer valuable insights into emergency hematopoiesis and therapeutic approaches against cancer. Exciting future directions for the study of EMH include identifying common and distinct EMH mechanisms in cancer, infectious diseases, and chronic autoimmune diseases to control these conditions.

Increased iron uptake by splenic hematopoietic stem cells promotes TET2-dependent erythroid regeneration

Hematopoietic stem cells (HSCs) are capable of regenerating the blood system, but the instructive cues that direct HSCs to regenerate particular lineages lost to the injury remain elusive. Here, we show that iron is increasingly taken up by HSCs during anemia and induces erythroid gene expression and regeneration in a Tet2-dependent manner. Lineage tracing of HSCs reveals that HSCs respond to hemolytic anemia by increasing erythroid output. The number of HSCs in the spleen, but not bone marrow, increases upon anemia and these HSCs exhibit enhanced proliferation, erythroid differentiation, iron uptake, and TET2 protein expression. Increased iron in HSCs promotes DNA demethylation and expression of erythroid genes. Suppressing iron uptake or TET2 expression impairs erythroid genes expression and erythroid differentiation of HSCs; iron supplementation, however, augments these processes. These results establish that the physiological level of iron taken up by HSCs has an instructive role in promoting erythroid-biased differentiation of HSCs.

Tissue Perfusion and Diffusion and Cellular Respiration: Transport and Utilization of Oxygen

This article provides an overview of the journey of inspired oxygen after its uptake across the alveolar-capillary interface, and the interplay among tissue perfusion, diffusion, and cellular respiration in the transport and utilization of oxygen. The critical interactions between oxygen and its facilitative carriers (hemoglobin in red blood cells and myoglobin in muscle cells), and with other respiratory and vasoactive molecules (carbon dioxide, nitric oxide, and carbon monoxide), are emphasized to illustrate how this versatile system dynamically optimizes regional convective transport and diffusive gas exchange. The rates of reciprocal gas exchange in the lung and the periphery must be well-matched and sufficient for meeting the range of energy demands from rest to maximal stress but not excessive as to become toxic. The mobile red blood cells play a vital role in matching tissue perfusion and gas exchange by dynamically regulating the controlled uptake of oxygen and communicating regional metabolic signals across different organs. Intracellular oxygen diffusion and facilitation via myoglobin into the mitochondria, and utilization via electron transport chain and oxidative phosphorylation, are summarized. Physiological and pathophysiological adaptations are briefly described. Dysfunction of any component across this integrated system affects all other components and elicits corresponding structural and functional adaptation aimed at matching the capacities across the entire system and restoring equilibrium under normal and pathological conditions.

Paratesticular Extramedullary Hematopoiesis in Children

CONTEXT.—

Extramedullary hematopoiesis (EMH) is an uncommon occurrence, usually associated with hematologic disorders, but it rarely presents as an isolated finding.

OBJECTIVE.—

To determine the frequency, immunomorphologic features, and clinicopathologic background of EMH in orchiectomies from pediatric patients.

DESIGN.—

All orchiectomy specimens removed from children from 2008 to 2020 in our institution were retrospectively reviewed. Biopsies and neoplasias were excluded. The EMH diagnosis was rendered when hematopoietic cell precursors were present. Immunohistochemical stainings were performed to characterize the hematopoietic components.

RESULTS.—

Seventy-nine orchiectomies from 77 children (mean age, 5 years; range, 0-17 years) were included in our study. Forty-three patients (55.8%) underwent surgery for testicular atrophy, 30 (39.0%) for torsion, and 4 (5.2%) for intersex conditions. EMH was identified in 6 of 79 orchiectomies (7.6%), all performed for testicular torsion. All patients but one were newborns, and the remaining patient was 15 years old. No patient had evidence of a hematologic disorder. All EMH foci were in a background of reactive changes with a variable extension, either in the epididymis (4 cases) or in the deferens duct (2 cases). Immunostaining confirmed an association of myeloid (myeloperoxidase+) and erythroid precursors (E-cadherin+) in all 6 cases. One case also presented rare megakaryocytes, and one showed benign TdT+ B-cell precursors.

CONCLUSIONS.—

To our knowledge, this is the first study that demonstrates EMH as a common finding in orchiectomy samples, especially from newborns. Despite the lack of pathologic potential, it is important to recognize EMH in order to avoid misdiagnosis.

Extramedullary hematopoietic pleural effusion in Waldenström's macroglobulinemia

Extramedullary hematopoietic effusion (EHE) is one of the extremely rare phenomena associated with extramedullary hematopoiesis, which is caused by serous effusions, including pleural effusion, and may be related to hematologic disorders and neoplasms. Herein, we present the case of an 81-year-old man with EHE accompanying Waldenström's macroglobulinemia (WM). The patient complained of anemia and dyspnea. The chest X-ray and computed tomography showed a massive left pleural effusion, and the aspirates revealed infiltration of the immature myeloid cells and megakaryocytes, in addition to the lymphoma cells. To our knowledge, this is the first report of EHE in WM.

Extramedullary hematopoiesis (EMH) in the liver allograft presenting with a mass-like lesion

This is a rare case of extramedullary hematopoiesis (EMH) presenting as a mass-like lesion in liver allograft. Our patient was a 57-year-old woman who had undergone liver transplantation due to hepatic epithelioid hemangioendothelioma. She presented with an ill-defined hypoechoic lesion on ultrasound which showed features of focal EMH on pathologic examinations. While transient intrahepatic hematopoiesis has been reported in liver transplant patients, focal EMH mass lesion is a rarely encountered phenomenon. Therefore, focal EMH may need to be considered as a differential diagnosis when encountering a mass in post liver transplant patients.

Extramedullary Hematopoiesis Adjacent to Vertebral Fracture in a Patient with Pernicious Anemia: Support for a Mechanical Extrusion Mechanism

CASE

A 68-year-old woman presented with a paraspinal mass of indeterminate imaging characteristics. Workup and computed tomography-guided Fine Needle Aspiration (FNA) aspiration revealed extramedullary hematopoiesis (EMH) adjacent to a prior compression fracture in the setting of pernicious anemia.

CONCLUSION

The combination of findings suggests a possible relationship of the compression fracture and the EMH because of traumatic extravasation of marrow contents, with the patient's underlying anemia possibly providing an underlying predisposition to EMH.

Extramedullary Hematopoiesis: A Forgotten Diagnosis and a Great Mimicker of Malignancy

ABSTRACT

Radiology errors have been reported in up to 30% of cases when patients have abnormal imaging findings. Although more than half of errors are failures to detect critical findings, over 40% of errors are when findings are recognized but the correct diagnosis or interpretation is not made. One common source of error is when imaging findings from one process simulate imaging findings from another process but the correct diagnosis is not made. This can result in additional imaging studies, unnecessary biopsies, or surgery. Extramedullary hematopoiesis is one of those uncommon disease processes that can produce many imaging findings that may lead to misdiagnosis. The objective of this article is to review the common and uncommon imaging features of extramedullary hematopoiesis while presenting a series of interesting relevant illustrative cases with emphasis on CT.

Coexisting Extra-Medullary Manifestation of Chronic Myelomonocytic Leukemia and Follicular Lymphoma What's Between Neoplastic Follicles Matters

We illustrate a rare case of coexisting extramedullary manifestation of CMML and new onset follicular lymphoma within the same core-needle biopsy of a lymph node. We discuss the differences between extramedullary hematopoiesis and extramedullary manifestation of myeloid neoplasms. We also highlight the importance of generous tissue sampling and thorough examination of nodal tissue in the setting of an established myeloid neoplasm to avoid missing rare but possible nodal involvement.

The Quantification and Significance of Extramedullary Hematopoiesis Seen on Liver Biopsy Specimens

OBJECTIVES

Extramedullary hematopoiesis (EMH) may occur in the liver and is often considered pathologic in adults. Many hematologic and nonhematologic disorders are associated with the development of EMH. However, it is unclear whether the presence of EMH is always pathologic. At present, no formal grading system for EMH in the liver exists.

METHODS

We reviewed 42 liver biopsy specimens with EMH and developed a novel grading system to quantify the degree of EMH from 1 to 3 based on the number of EMH foci in 10 high-power fields.

RESULTS

Most patients had nonhematologic conditions (n = 25). Seventeen patients had a hematologic condition, most frequently a myeloproliferative neoplasm (n = 9). Patients with an underlying hematologic condition had a significantly higher EMH grade compared with those without a hematologic condition (P < .0001). All patients with grade 3 EMH had an underlying hematologic diagnosis, and most (86%) patients with grade 1 EMH had a nonhematologic disorder.

CONCLUSIONS

Our data suggest that EMH grading in the liver is feasible and can identify patients who may have an underlying hematologic condition, which can guide further diagnostic workup.

An Unusual Case of Myelodysplastic Syndrome With Intrahepatic Extramedullary Hematopoiesis Leading to Liver Failure

We present a rare case of a 61-year-old male who arrived at the hospital with fatigue and was found to have pancytopenia. Following further workup, he was diagnosed with myelodysplastic syndrome. His initial bilirubin of 3.1 mg/dL rose to 38.0 mg/dL. After a liver biopsy was obtained, intrahepatic extramedullary hematopoiesis (EMH) was diagnosed and showed the liver to be infiltrated by EMH without malignancy. Within 16 days of his stay, he developed liver failure and passed away. Although intrahepatic EMH is uncommon, EMH resulting in infiltration, liver failure, and then death is exceedingly rare.

Paravertebral extramedullary hematopoiesis in a case of myelodysplastic syndrome with ring sideroblasts and an SF3B1 mutation

We present the case of a 56-year-old male patient with paravertebral extramedullary hematopoiesis (EMH) secondary to myelodysplastic syndrome with ring sideroblasts and multilineage dysplasia. In a routine health checkup over 5 years prior, he presented with asymptomatic mild anemia and a posterior mediastinal mass. Pathological and cytomorphological findings of the resected paravertebral mass were similar to those of his bone marrow specimen, and included cellularity with erythroid hyperplasia, multilineage dysplastic changes, and the presence of ring sideroblasts. A concordant SF3B1 mutation was detected in both bone marrow and paravertebral mass samples, suggesting that the EMH cells were derived from the bone marrow.

Extramedullary Hematopoiesis of the Liver and Spleen

Hematopoiesis is the formation of blood cellular components and, consequently, immune cells. In a more complete definition, this process refers to the formation, growth, maturation, and specialization of blood cells, from the hematopoietic stem cell, through the hematopoietic progenitor cells, to the s pecialized blood cells. This process is tightly regulated by several elements of the bone marrow microenvironment, such as growth factors, transcription factors, and cytokines. During embryonic and fetal development, hematopoiesis takes place in different organs: the yolk sac, the aorta–gonad mesonephros region, the lymph nodes, and not lastly, the fetal liver and the spleen. In the current review, we describe extramedullary hematopoiesis of the spleen and liver, with an emphasis on myeloproliferative conditions.

Fine-needle aspiration diagnosis of clonal extramedullary hematopoiesis in a case of myeloproliferative neoplasm

Extramedullary hematopoiesis (EMH)-the proliferation of hematopoietic progenitors outside of the bone marrow (BM) is a well-known phenomenon in myeloproliferative neoplasms (MPN). Abundant literature describes EMH at various body sites in cases of MPN, and some studies showed the presence of cytogenetic changes associated with MPN in the EMH tissues. We present a case of an 80-year-old female, with a history of MPN, presenting with mediastinal adenopathy. The transbronchial fine-needle aspiration (FNA) of the mediastinal lymph node showed EMH with atypical megakaryocytes and del(13q) demonstrated by fluorescence in situ hybridization. The subsequent BM biopsy demonstrated myelofibrosis with atypical megakaryocytes harboring the same cytogenetic abnormality. Our case highlights the capability of FNA cytology for providing accurate morphologic, immunohistochemical, and cytogenetic diagnosis of clonal EMH.

Extramedullary Hematopoiesis Presenting with Thoracic Spinal Cord Compression in a Young Adult with Thalassemia Major: A Case Report

BACKGROUND

Extramedullary hematopoiesis (EMH) refers to the production of blood cellular components at sites other than the bone marrow, namely liver, spleen, and lymph nodes. The common sites associated with this condition are the liver, spleen, and lymph nodes whereas the common conditions associated with it are myelofibrosis, myelodysplasia, thalassemia, sickle cell anemia, and polycythemia vera.

CASE DESCRIPTION

This report describes a young male with thalassemia major, who presented with symptomatic cord compression due to a thoracic intraspinal lesion. It was surgically excised and diagnosed as a case of EMH. The boy recovered fully and has been asymptomatic for six months now.

CONCLUSION

The occurrence of EMH in the thoracic spine is uncommon, whereas symptomatic cord compression as a result of it is even more unusual. Magnetic resonance imaging (MRI) is the diagnostic imaging of choice and treatment options that can be offered are surgical decompression, radiotherapy, hydroxyurea, and transfusion of packed red blood cells (RBCs).

Sex Matters: Physiological Abundance of Immuno-Regulatory CD71+ Erythroid Cells Impair Immunity in Females

Mature erythrocytes are the major metabolic regulators by transporting oxygen throughout the body. However, their precursors and progenitors defined as CD71+ Erythroid Cells (CECs) exhibit a wide range of immunomodulatory properties. Here, we uncover pronounced sexual dimorphism in CECs. We found female but not male mice, both BALB/c and C57BL/6, and human females were enriched with CECs. CECs, mainly their progenitors defined as CD45+CECs expressed higher levels of reactive oxygen species (ROS), PDL-1, VISTA, Arginase II and Arginase I compared to their CD45- counterparts. Consequently, CECs by the depletion of L-arginine suppress T cell activation and proliferation. Expansion of CECs in anemic mice and also post-menstrual cycle in women can result in L-arginine depletion in different microenvironments in vivo (e.g. spleen) resulting in T cell suppression. As proof of concept, we found that anemic female mice and mice adoptively transferred with CECs from anemic mice became more susceptible to Bordetella pertussis infection. These observations highlight the role of sex and anemia-mediated immune suppression in females. Notably, enriched CD45+CECs may explain their higher immunosuppressive properties in female BALB/c mice. Finally, we observed significantly more splenic central macrophages in female mice, which can explain greater extramedullary erythropoiesis and subsequently abundance of CECs in the periphery. Thus, sex-specific differences frequency in the frequency of CECs might be imprinted by differential erythropoiesis niches and hormone-dependent manner.

Evaluation of splenic accumulation and colocalization of immature reticulocytes and Plasmodium vivax in asymptomatic malaria: A prospective human splenectomy study

BACKGROUND

A very large biomass of intact asexual-stage malaria parasites accumulates in the spleen of asymptomatic human individuals infected with Plasmodium vivax. The mechanisms underlying this intense tropism are not clear. We hypothesised that immature reticulocytes, in which P. vivax develops, may display high densities in the spleen, thereby providing a niche for parasite survival.

METHODS AND FINDINGS

We examined spleen tissue in 22 mostly untreated individuals naturally exposed to P. vivax and Plasmodium falciparum undergoing splenectomy for any clinical indication in malaria-endemic Papua, Indonesia (2015 to 2017). Infection, parasite and immature reticulocyte density, and splenic distribution were analysed by optical microscopy, flow cytometry, and molecular assays. Nine non-endemic control spleens from individuals undergoing spleno-pancreatectomy in France (2017 to 2020) were also examined for reticulocyte densities. There were no exclusion criteria or sample size considerations in both patient cohorts for this demanding approach. In Indonesia, 95.5% (21/22) of splenectomy patients had asymptomatic splenic Plasmodium infection (7 P. vivax, 13 P. falciparum, and 1 mixed infection). Significant splenic accumulation of immature CD71 intermediate- and high-expressing reticulocytes was seen, with concentrations 11 times greater than in peripheral blood. Accordingly, in France, reticulocyte concentrations in the splenic effluent were higher than in peripheral blood. Greater rigidity of reticulocytes in splenic than in peripheral blood, and their higher densities in splenic cords both suggest a mechanical retention process. Asexual-stage P. vivax-infected erythrocytes of all developmental stages accumulated in the spleen, with non-phagocytosed parasite densities 3,590 times (IQR: 2,600 to 4,130) higher than in circulating blood, and median total splenic parasite loads 81 (IQR: 14 to 205) times greater, accounting for 98.7% (IQR: 95.1% to 98.9%) of the estimated total-body P. vivax biomass. More reticulocytes were in contact with sinus lumen endothelial cells in P. vivax- than in P. falciparum-infected spleens. Histological analyses revealed 96% of P. vivax rings/trophozoites and 46% of schizonts colocalised with 92% of immature reticulocytes in the cords and sinus lumens of the red pulp. Larger splenic cohort studies and similar investigations in untreated symptomatic malaria are warranted.

CONCLUSIONS

Immature CD71+ reticulocytes and splenic P. vivax-infected erythrocytes of all asexual stages accumulate in the same splenic compartments, suggesting the existence of a cryptic endosplenic lifecycle in chronic P. vivax infection. Findings provide insight into P. vivax-specific adaptions that have evolved to maximise survival and replication in the spleen.

15-PGDH inhibition activates the splenic niche to promote hematopoietic regeneration

The splenic microenvironment regulates hematopoietic stem and progenitor cell (HSPC) function, particularly during demand-adapted hematopoiesis; however, practical strategies to enhance splenic support of transplanted HSPCs have proved elusive. We have previously demonstrated that inhibiting 15-hydroxyprostaglandin dehydrogenase (15-PGDH), using the small molecule (+)SW033291 (PGDHi), increases BM prostaglandin E₂ (PGE₂) levels, expands HSPC numbers, and accelerates hematologic reconstitution after BM transplantation (BMT) in mice. Here we demonstrate that the splenic microenvironment, specifically 15-PGDH high-expressing macrophages, megakaryocytes (MKs), and mast cells (MCs), regulates steady-state hematopoiesis and potentiates recovery after BMT. Notably, PGDHi-induced neutrophil, platelet, and HSPC recovery were highly attenuated in splenectomized mice. PGDHi induced nonpathologic splenic extramedullary hematopoiesis at steady state, and pretransplant PGDHi enhanced the homing of transplanted cells to the spleen. 15-PGDH enzymatic activity localized specifically to macrophages, MK lineage cells, and MCs, identifying these cell types as likely coordinating the impact of PGDHi on splenic HSPCs. These findings suggest that 15-PGDH expression marks HSC niche cell types that regulate hematopoietic regeneration. Therefore, PGDHi provides a well-tolerated strategy to therapeutically target multiple HSC niches, promote hematopoietic regeneration, and improve clinical outcomes of BMT.

Contribution of Extramedullary Hematopoiesis to Atherosclerosis. The Spleen as a Neglected Hub of Inflammatory Cells

Cardiovascular diseases (CVDs) incidence is becoming higher. This fact is promoted by metabolic disorders such as obesity, and aging. Atherosclerosis is the underlying cause of most of these pathologies. It is a chronic inflammatory disease that begins with the progressive accumulation of lipids and fibrotic materials in the blood-vessel wall, which leads to massive leukocyte recruitment. Rupture of the fibrous cap of the atherogenic cusps is responsible for tissue ischemic events, among them myocardial infarction. Extramedullary hematopoiesis (EMH), or blood cell production outside the bone marrow (BM), occurs when the normal production of these cells is impaired (chronic hematological and genetic disorders, leukemia, etc.) or is altered by metabolic disorders, such as hypercholesterolemia, or after myocardial infarction. Recent studies indicate that the main EMH tissues (spleen, liver, adipose and lymph nodes) complement the hematopoietic function of the BM, producing circulating inflammatory cells that infiltrate into the atheroma. Indeed, the spleen, which is a secondary lymphopoietic organ with high metabolic activity, contains a reservoir of myeloid progenitors and monocytes, constituting an important source of inflammatory cells to the atherosclerotic lesion. Furthermore, the spleen also plays an important role in lipid homeostasis and immune-cell selection. Interestingly, clinical evidence from splenectomized subjects shows that they are more susceptible to developing pathologies, such as dyslipidemia and atherosclerosis due to the loss of immune selection. Although CVDs represent the leading cause of death worldwide, the mechanisms involving the spleen-atherosclerosis-heart axis cross-talk remain poorly characterized.

Lenograstim-Induced Nodal Extramedullary Hematopoiesis: A Challenging Diagnosis in Lymphoma Evaluation With 18F-FDG PET/CT

We report the case of a 23-year-old man with nodal EMH (extramedullary hematopoiesis) occurring during treatment for a stage IIA "gray-zone" lymphoma. Although it is often related to myeloproliferative bone marrow disease, benign etiologies such as lenograstim treatment after chemotherapy can also induce EMH and be responsible for false-positive F-FDG PET/CT examinations. In this respect, GLUT overexpression in hematopoietic lineages and macrophages of the inflammatory environment are responsible for increased F-FDG uptake. Histopathologic confirmation of new hypermetabolic lesions on follow-up PET/CT may be required when the new lesions do not conform with the treatment responses in the preexisting lesions.

Myeloid, mast cell, histiocytic and dendritic cell neoplasms and proliferations involving the spleen

Splenic involvement and consequent splenomegaly are usually seen as part of systemic involvement by myeloid neoplasms as well as mast cell and histiocytic neoplasms. Primary splenic involvement by these neoplasms is rare. Splenectomy is usually not performed for establishing a diagnosis of these entities. However, in rare instances, the pathologist may need to evaluate the spleen secondary to splenic rupture or palliative splenectomy to alleviate symptoms related to splenomegaly. This review article describes the clinicopathologic features of a broad group of myeloid, mastocytic, and histiocytic proliferative and neoplastic disorders.

Primary and secondary diseases of the perinephric space: an approach to imaging diagnosis with emphasis on MRI

The perinephric space is the middle compartment of the retroperitoneum, containing the kidneys and adrenal glands. Differential considerations for diseases involving primarily the perinephric space differ from those arising from the kidney itself, show variant imaging features, and require identification and characterisation by interpreting radiologists-an imaging diagnosis can be suggested in many cases. Lymphangiomas are congenital cystic lesions that may contain lipid-laden chyle, which may be detectable on magnetic resonance imaging (MRI). Retroperitoneal fibrosis, Erdheim-Chester disease, and lymphoma may present as a perinephric soft tissue rind. Osseous findings favour Erdheim-Chester, ureteric obstruction favours retroperitoneal fibrosis, and associated lymphadenopathy with mass-effect, but without invasion of adjacent structures favours lymphoma. Extramedullary haematopoiesis and brown fat stimulation are both characterised by signal drop on opposed-phase T1-weighted (W) images, the former resulting from severe anaemia and the latter in the context of elevated serum catecholamines, especially in the setting of phaeochromocytoma. Liposarcoma is the most common primary sarcoma of the retroperitoneum. Metastases are uncommon; however, they can be seen in melanoma, among other primary malignancies. Increased T1W signal hyperintensity is typical of melanoma metastases and haematomas. Abscesses show non-enhancing fluid centrally with marked diffusion restriction. This article presents a review of the perinephric space, pathological conditions of the perinephric space, and an approach towards imaging and diagnosis using cross-sectional imaging, with emphasis on MRI. MRI provides better tissue characterisation, assessment of enhancement kinetics, and detection of intralesional fat in comparison to CT. Clinical and laboratory correlation or tissue sampling may be required for definitive diagnosis in some cases.

The mechanisms of pathological extramedullary hematopoiesis in diseases

Extramedullary hematopoiesis (EMH) is the expansion and differentiation of hematopoietic stem and progenitor cells outside of the bone marrow. In postnatal life, as a compensatory mechanism for ineffective hematopoiesis of the bone marrow, pathological EMH is triggered by hematopoietic disorders, insufficient hematopoietic compensation, and other pathological stress conditions, such as infection, advanced tumors, anemia, and metabolic stress. Pathological EMH has been reported in many organs, and the sites of pathological EMH may be related to reactivation of the embryonic hematopoietic structure in these organs. As a double-edged sword (blood and immune cell supplementation as well as clinical complications), pathological EMH has been widely studied in recent years. In particular, pathological EMH induced by late-stage tumors contributes to tumor immunosuppression. Thus, a deeper understanding of the mechanism of pathological EMH may be conducive to the development of therapies against the pathological processes that induce EMH. This article reviews the recent progress of research on the cellular and molecular mechanisms of pathological EMH in specific diseases.

Splenic extramedullary hematopoiesis in dogs is frequently detected on multiphase multidetector-row CT as hypervascular nodules

Extramedullary hematopoiesis (EMH) is the formation and development of blood cells outside the bone marrow, and in dogs it frequently occurs in the spleen. Although splenic EMH is a relatively common condition, data regarding its appearance in veterinary medicine are lacking. Our aim was to describe different multidetector computed tomographic (MDCT) features of splenic EMH in dogs. In this descriptive retrospective study, dogs with cytological diagnosis of splenic EMH and three-phase MDCT study of the abdomen were included. Multi-detector CT findings recorded were splenomegaly, appearance of the parenchyma, and mean attenuation of the spleen and lesions. Out of 89 dogs included, 55 (62%) presented multifocal nodular aspect, 14 (16%) mass, 12 (13%) diffuse heterogeneous parenchyma, and eight (9%) normal spleen. Most lesions were hyperattenuating to the parenchyma in the arterial (57/89, 64%) and portal (59/89, 66%) phases; whereas in the interstitial phase only 40 of 89 (45%) were hyperattenuating. The mean attenuations of the lesions were higher compared to the values of the adjacent spleen, and the difference of the mean attenuation between the hyperattenuating lesions and the parenchyma was significantly higher in arterial and portal phases than in interstitial phase (P < .0001). The most frequent MDCT aspect of splenic extramedullary hematopoiesis consists of multiple nodules hyperattenuating to the normal spleen, best visualized in the arterial and portal phases.

A case report of a rare omental extramedullary hematopoiesis in an adult: 'an idiopathic finding'

This is a case of a 62-year-old female, known to have multiple medical problems, who presented to her primary care physician with an intermittent abdominal pain and discomfort for a few months. The initial work-up showed mild leucocytosis and a small mass in the omentum. Given that the most concerning differential diagnosis was malignancy, the patient was referred to oncology, where biopsy of the mass showed omentum extramedullary hematopoiesis. The differential diagnosis was wide; however, a repeat computed tomography (CT) scan of the abdomen and pelvis did show persistence of the omental mass. After ruling out any possible causes, including myelofibrosis, with a normal bone marrow, her extramedullary hematopoiesis was deemed of unknown origin and with no clear explanation. Therefore, the patient was diagnosed with a rare adult idiopathic omental extramedullary hematopoiesis that was stable over time.