Case 353

Submitting Author: Cetin, Neslihan, MD
Institution: University of Arkansas for Medical Sciences, Arkansas Children's Hospital
Additional authors:Murat Gokden MD, Robert Lorsbach MD PhD
Session: Extramedullary manifestations of myeloid neoplasms

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HISTORY

A 16 year-old male with no significant past medical history presented with a 3 day history of inability to move his lower extremities. MRI showed an epidural mass from C6 to T6 with spinal cord compression. The patient underwent a posterior thoracic decompression and resection of the lesion. The preoperative diagnosis was ganglioneuroma or schwannoma.

DETAILS

H&E-stained sections of the epidural lesion showed a monotonous infiltrate of intermediate-sized cells with open chromatin, and prominent nucleoli; admixed maturing myeloid cells were not apparent. Many mitotic figures and apoptotic cells were noted.

IMMUNOHISTOCHEMISTRY AND FLOW CYTOMETRY

Immunohistochemical stains were performed on formalin-fixed, paraffin-embedded sections. The neoplastic cells were positive for CD45, CD43, CD117, CD56, CD34 (subset). They were negative for TdT, synaptophysin, myogenin, desmin, neurofilament, CD10, CD20, BCL-6, cyclin-D1, CD3, and CD20. Based on the immunophenotype, a diagnosis of myeloid sarcoma was rendered. Subsequent laboratory work-up revealed leukocytosis (19.6 x 109/L) with 75% blasts, anemia (hemoglobin 10 g/dl) and thrombocytopenia (platelet count 84 x 109/L). Flow cytometric analysis performed on peripheral blood identified 70% blasts with monocytic differentiation, which were positive for HLA-DR, CD34, CD117, CD33, CD19, MPO, CD13 (subset), CD15 (subset).

CYTOGENETIC FINDINGS

Cytogenetics revealed 46, X, -Y, add(9)(q22),ins(21;8)(q22;q22q22)[17]/46,XY[3].

MOLECULAR FINDINGS

Bone marrow aspirate FISH analysis confirmed a cryptic translocation of RUNX1-RUNX1T1.

INTERESTING FEATURES

The diagnosis of myeloid sarcoma was unexpected given the lack of prior history of leukemia and sudden loss of lower extremity movement due to epidural mass. In this case, myeloid sarcoma was associated with concurrent acute myeloid leukemia with monocytic differentiation based on flow cytometric immunophenotype. Myeloid sarcomas not infrequently present at unusual anatomic sites and are frequently diagnostically challenging, particularly in patients without a history of AML or myeloproliferative neoplasm. They should always be included in the differential of poorly differentiated mass lesions where the diagnosis is not readily apparent. Although the molecular genetics of the extramedullary tumor was not assessed, the bone marrow aspirate cells were positive for RUNX1-RUNX1T1 fusion.

PROPOSED DIAGNOSIS

Myeloid sarcoma

CONSENSUS DIAGNOSIS

Acute myeloid leukemia with cryptic translocation of RUNX1-RUNX1T1 involving bone marrow and spinal mass (myeloid sarcoma)