Introduction
Myeloid sarcoma is a tumor mass consisting of myeloid blasts, with or without maturation, occurring in an anatomical site other than bone marrow.1
Myeloid Sarcoma (MS) is only called so if there is a mass formation with complete effacement of tissue architecture.
More than 2000 cases have been reported so far, with about 21% cases occurring in the mediastinum.2
Clinical features depend on the location, with symptoms due to tumor mass effect or local organ dysfunction. It may sometimes precede/ coincide with AML or constitute blastic transformation of MDS/ MPN.1
Case Report
A 17-year-old female came with the complaints of swelling in the neck since 1 month, breathlessness for the past 5 days.
Pet-CT
Metabolically active disease in the large soft tissue mass occupying the entire mediastinum, encasing the mediastinal vessels, trachea and esophagus.
Metabolically active disease in the large ill-defined soft tissue mass in bilateral supraclavicular region.
Mild pleural effusion and pericardial effusion.
Metabolic activity in the cardiophrenic nodes.
Diffuse hypermetabolism in the marrow of all bones of axial and proximal appendicular skeleton.
Pericardiocentesis
Appearance: Turbid
Color: Red
Coagulum: Present
Cell count: 74,000 cells/cumm
Cell type: Mononuclear atypical cells: 90%
Neutrophils: 10%
Protein: 6.8 g/dL
Glucose: 10 mg/dL
Myelopoiesis: Increased in number, shows predominant population of blasts (86%), having high N:C ratio, fine chromatin, 1-2 nucleoli, scanty cytoplasm. Few blasts are seen to have nuclear convolutions.
Impression: Acute Leukemia, immunophenotyping indicated for further subtyping.
Discussion
Myeloid sarcoma is a rare neoplasm with a greater chance of it being misdiagnosed as malignant lymphoproliferative disorders including Hodgkin’s lymphoma, MALT lymphoma, DLBCL, Ewing’s sarcoma, thymoma, round blue cell tumors or poorly differentiated carcinoma.3 The misdiagnosis was commonly due to inadequate immunophenotyping of the MS lesion and was not corrected until a diagnosis of acute leukemia was later established by bone marrow biopsy or peripheral blood examination.4
In a study by J E Takasugi et.al, mediastinum was the commonest intrathoracic site for MS and 6 out of 9 cases presented with pleural effusion.5
Very few cases of MS with pleural and pericardial effusion have been reported.
Conclusion
Recognition of MS with or without AML is necessary for prognosis.
Correlating radiological, hematological, bone marrow and flowcytometry features with histomorphology and immunohistochemistry of the tumor is essential.
A rare possibility of MS should be kept in mind for mediastinal masses for timely diagnosis and treatment.
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