Chloroma - acute myeloid leukemia
Presenting with several week history of left temporal headache. Prior sibling allogenic stem cell transplant 2 years ago for AML.
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4.8 cm x 3.2 cm (axial) x 2.9 cm (craniocaudal) heterogenous mass centered in the anterior left temporal lobe. The crescentic peripheral portion of the lesion demonstrates hyperattenuation relative to the remainder of the brain parenchyma on noncontrast study and demonstrates avid enhancement on post-contrast imaging. Low attenuation centrally in the lesion consistent with necrosis.
Surrounding vasogenic edema, most pronounced in the left temporal and parietal lobes with associated mass effect, with effacement of the sulcal pattern of the left temporal and parietal lobes, slight effacement of the left basal ganglia, basal cisterns, and of the left lateral ventricle; with minimal (2 mm) left-to-right midline shift.
Sclerotic changes noted in the anterior left temporal bone with evidence of transosseous extension of tumor better seen on the MRI.
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5.8 (AP) x 3.4 (Tran) x 2.9 (cc) cm rim-enhancing mass within the anterior inferior left temporal fossa which appears to have a dural tail extending along the surface of Meckel's cave, suggesting that this is an extra-axial dural-based mass with probable intra-axial extension in the left temporal lobe. The mass demonstrates heterogenous predominantly isointense signal on T2 weighted imaging and is mildly hypointense on T1 weighted imaging. There is some reduced diffusion within the within the solidly enhancing components of the mass, compatible with hypercellular tumor. Transosseous extension of enhancement into the infratemporal fossa and into the deep aspect of the temporalis muscle with bony changes better seen on the CT. Scattered punctate foci of susceptibility artifact consistent with hemorrhage.
Associated vasogenic edema and mass effect with deviation of the left middle cerebral artery anteriorly, minimal effacement of the left lateral ventricle and unchanged minimal midline shift to the right by approximately 5 mm with slight compression of the left cerebral peduncle and minimal left uncal herniation.
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Micrographs A-C: Left temporal lobe tumor. Primitive-appearing blue cell neoplasm, large areas of necrosis, and fragments of brain parenchyma. Neoplastic cells have round to angulated, pleomorphic, hyperchromatic nuclei associated with scant amounts of cytoplasm and are arranged in sheets. There are numerous mitoses.
C: Left temporal lobe tumor staining positively for MPO.
D: Left temporal lobe tumor staining positively for CD 117.
E. Sections of cancellous left temporal bone bone show deposits of primitive appearing small blue cell neoplasm in the marrow space, morphologically similar, with features of remodeling.
F. Sections of skeletal (left temporalis) muscle and connective tissue show similar morphology to the myeloid sarcoma in the left temporal lobe. MPO immunohistochemistry is diffusely positive in infiltrating cells.
MPO: Diffusely positive.
CD117: Diffuse positivity, mildly patchy.
Synaptophysin: Highlights neuropil in areas of invasion.
CD68: Largely negative.
CD3: Highlights reactive background T cells.
Myeloid sarcoma (MS), or granulocytic sarcoma, is a tumoral lesion consisting of immature myeloid cells, mainly myeloblasts of granulocytic series - representing a focal accumulation of leukemic cells. Also known as chloroma due to its green color attributed to the enzyme myeloperoxidase (MPO) 1.
Sites of isolated myeloid sarcoma include lymph nodes, bone, periosteum and soft tissues, and less commonly the orbit, epidural brain/spine, mediastinum, intestine, uterus, and ovary 2-6.
Myeloid sarcoma is detected simultaneously with the diagnosis of AML in 1% of cases 7 or during the course of the disease, and also at relapses after allogeneic stem cell transplantation.
Four different patterns of myeloid sarcoma development in AML patients:
- during the active phase of leukemia
- concurrently with known chronic myeloproliferative disorders
- manifesting as relapse after months or years after clinical remission of AML, particularly after bone marrow transplantation
- preceding the AML diagnosis and may be detected in previously healthy patients who have a normal peripheral blood cell count and who have no blast infiltration in the bone marrow 8
Less commonly myeloid sarcoma is associated with myelodysplastic syndrome, chronic myeloid leukemia and other myeloproliferative diseases.
The key components to the diagnosis, in this case, are the clinical history of AML, extra-axial location and cellular appearance of the tumor on diffusion-weighted and post-contrast imaging and histological positive stains for myeloperoxidase (MPO) and CD117 which differentiates it from other small round blue cell tumors such as Ewing sarcoma.
The current treatment recommendation for isolated myeloid sarcoma and myeloid sarcoma occurring in AML patients is AML-type chemotherapy 9.
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