Focal extramedullary hematopoiesis in the spleen: case report

¹Radiology Department, Arrazi Hospital, Mohammed VI University Hospital, Marrakech, Morocco

^&Corresponding author
Youssef Bouktib, Radiology Department, Arrazi Hospital, Mohammed VI University Hospital, Marrakech, Morocco

Introduction    

Extramedullary hematopoiesis (EMH) occurs as a compensatory mechanism when the bone marrow's ability to produce blood cells is inadequate, leading to its manifestation in various organs, this entity remains rare. However, its appearance as a localized mass within the spleen is uncommon. Prior studies have shown that such focal splenic masses from EMH may exhibit minimal to no enhancement following the administration of contrast material. In this report, we describe a case of EMH.

Patient and observation     

Patient information: a 51-year-old male, non-smoker, non-alcoholic, hypertensive and sedentary.

Clinical findings: petechiae and ecchymoses on both his forearms and lower legs.

Timeline of current episode: March 2023 underwent several imaging tests, including MRI. Sonography August 2023: biopsy, histology, and immunohistochemical studies were conducted.

Diagnostic assessment: CBC" (complete blood count): severe thrombocytopenia detected in an outpatient setting (white blood cell count: 8000/mm³; hemoglobin: 9.6 g/dL; platelets: 4x10⁹/L; prothrombin time: 11.4/11.5 seconds; partial thromboplastin time: 22.8/31.5 seconds). Sonography identified a clearly defined, solitary hyperechoic lesion in the spleen measuring approximately 5 cm (Figure 1). Magnetic resonance imaging (MRI) imaging characterized the lesions as a round, thin-walled encapsulated mass within the spleen. It was isointense in T1-weighted images and slightly hypointense in T2-weighted images (Figure 2). Post-gadolinium, the two lesions showed consistent enhancement across arterial, portal venous, and delayed phases, except for its central zone, which did not enhance during the arterial phase but showed delayed contrast filling in later phases (Figure 3). Biopsy, histology sections, and immunohistochemistry of the removed spleen mass (Figure 4) indicated: that it consisted of clusters of immature myeloid and erythroid cells, encased within a thin fibrous capsule, and featured a central area that was eosinophilic and displayed low cell density. Detailed examination using high-power microscopy identified the composition of the mass as including blood vessels, precursors to myeloid and erythroid cells, megakaryocytes, and extracellular hemosiderin deposits.

Diagnosis: the diagnosis established was extramedullary hematopoiesis (EMH) in the spleen. The initial differential diagnosis considered inflammatory pseudotumor, splenic hamartoma, and low-grade lymphoma.

Therapeutic interventions: he was treated with a blood transfusion, and splenectomy.

Follow-up and outcome of interventions: the patient had an excellent clinical progression, he remains asymptomatic and in excellent clinical condition.

Patient perspective: ”I expect to be cured, given that some conditions have completely disappeared, and I continue with clinical follow-up”.

Informed consent: the patient gave informed consent.

Discussion     

Extramedullary hematopoiesis (EMH) serves as a backup process that kicks in when the bone marrow fails to produce an adequate amount of blood cells, leading to the formation of hematopoietic precursors in non-typical locations. Extramedullary hematopoiesis is most commonly observed as microscopic diffuse infiltration in various sites, particularly in the liver and spleen. The occurrence of EMH as a distinct mass within the spleen is unusual [1]. There are limited reports in literature regarding the magnetic resonance (MR) characteristics of EMH, and to our knowledge, the presentation of EMH with delayed central enhancement in MR imaging has not been previously documented. This unique MR imaging signature of EMH has been confirmed through pathological examination [1,2]. The MR signal characteristics of EMH vary based on the stage of hematopoiesis and the activity level of the hematopoietic lesions. Lesions with active hematopoiesis, containing either immature or mature erythroid and myeloid cells, typically show intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images [3]. Conversely, older inactive lesions may demonstrate low signal intensity on both T1 and T2-weighted images due to iron deposition, or high signal intensity in cases of predominant fatty infiltration. In the inactive phase of EMH, the lesions do not enhance with gadolinium [4,5].

The atypical enhancement pattern observed in our case after gadolinium administration is attributed to the histological characteristics of the splenic mass, which included neovascular content likely responsible for the contrast enhancement in arterial phase images. The central zone's thick collagen bundles did not enhance in arterial phase images; however, contrast material gradually diffused into these hypocellular collagenous areas in delayed images. Due to the rarity and unique MR features of this condition, diagnosing EMH preoperatively was challenging. A definitive diagnosis of focal EMH in the spleen requires histopathological confirmation from a fine needle biopsy or surgical resection. Treatment may not always be necessary unless symptomatic. Options such as resection, radiotherapy, erythropoietin administration, and regular blood transfusions have been explored in managing EMH [5].

In summary, gadolinium-enhanced MRI plays a crucial role in the assessment of splenic masses, particularly when atypical imaging features are present. EMH, especially with peculiar delayed central enhancement, should be considered in the differential diagnosis of a splenic mass. The unique enhancement pattern observed in this case can be explained by the presence of a central hypocellular collagenous stroma in the EMH [6,7].

Conclusion     

Extramedullary hematopoiesis remains a very rare entity. The diagnosis is standardized based on clinical and radiological elements, which remain non-specific. Definitive diagnosis is based on histopathological examination.

Competing interests     

The authors declare no competing interest.

Authors' contributions     

All the authors have read and agreed to the final manuscript

Figures     

Figure 1: (A,B) a clearly defined rounded , solitary hyperechoic lesion in the spleen measuring approximately 5 cm

Figure 2: magnetic resonance imaging revealed a round thin encapsulated splenic mass; A) this splenic mass (arrow) was isointense on T1 weighted images; B) slightly hypointense on T2 weighted images

Figure 3: gadolinium-enhanced T1 weighted images demonstrated good homogeneous enhancement of the thin capsulated splenic mass on; A) arterial phase images; B) persisted into the portal venous; C) delayed phase images; the central zone (arrow) of the splenic mass did not enhance on arterial phase images

Figure 4: (A,B) granular cell and erythroid cell proliferations were noted in the tumor (hematoxylin and eosin stain, immunohistochemistry tests indicated positive results for CD 71 CD 41, myeloperoxidase, and hematopoietic cells such as erythroblasts, granulocytes, and megakaryocytes (×20)

References