Extramedullary Hematopoiesis in the Perinephric Region in a Case of Acute Myeloid Leukemia

We report the case of a 34-year-old male who died after an alleged fall from the staircase and an intracranial hematoma. An autopsy was conducted. This patient had acute myeloid leukemia, with the bone marrow showing 62% blasts. The blasts were myeloperoxidase (MPO) & CD117 positive on immunohistochemistry. The last peripheral smear showed 87% blasts. He died before the initiation of therapy.

The autopsy showed infiltration of the perinephric far spaces. The microscopic examination revealed an area of extramedullary hematopoiesis (EMH) with numerous erythroid colonies, few myeloid cells, and a significant population of megakaryocytes. The lesion was not encapsulated and on gross examination was unremarkable with no mass lesion [Figure 1a-c].

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Figure 1:

(a) Gross image of the cross-section of the kidney with the perinephric fat (no mass forming lesion). (b) Hematoxylin and Eosin stained sections show sheets of erythroid, myeloid and, megakaryocytic series of cells with peripheral rim of normal renal parenchyma (red arrow) (magnification: 40x). (c) Hematoxylin and Eosin-stained sections show sheets of erythroid, Myeloid and; Megakaryocytic (red arrow) series of cells (magnification: 100x). (d) Glycophorin immunohistochemistry highlights the erythroid series of cells (red arrow) (magnification: 100x). (e) CD61 highlights the megakaryocytic series of cells (red arrow) (magnification: 100x).

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Immunohistochemistry showed glycophorin, highlighting the erythroid series; MPO, highlighting the myeloid series; and CD61, highlighting the megakaryocytes. [Figure d and e] CD34 and CD117, initially positive in the marrow blasts, were negative.

The main differential diagnoses were myeloid sarcoma and extra-adrenal myelolipoma. Although myeloid sarcoma was possible, the preponderance of erythroid and megakaryocytic series of cells, along with the relative absence of blasts, eliminated this possibility. Also, the absence of a mass-forming lesion was against this diagnosis.^1-4

The patients with EMH present with anemia and thrombocytopenia with splenomegaly. They can be of any age and don’t usually present with a mass-forming lesion. The patients with extra-adrenal myelolipoma are generally >40 years with a normal hematological workup, no hepatosplenomegaly. They almost always present with mass-forming lesion and are generally associated with chronic debilitating conditions and endocrinopathies.^4,5

EMH is generally known to occur in the liver, spleen, and lymph nodes. It can also occur in other sites such as the adrenal gland, breast, female genital tract, prostate, and kidney.⁶ There are few case reports on EMH in the kidney. As such, the presence of EMH in the perinephric region is unique and unusual.⁷