A 2-year-old girl presented to the emergency department after weeks of fever, sweats, fatigue, and pallor. Chest CT and MRI revealed a right mediastinal mass with pericardial involvement (Figure). Pathologic findings corresponded to a group M primary malignant mediastinal histiocytic neoplasm. Genetic evaluation revealed mutations in the BRAF V600E and CDKN2A tumor suppressor genes. The patient responded to targeted BRAF inhibitors dabrafenib and later, trametinib. The tumor shrunk over 2 years.
Images in a 2-year-old girl with a primary malignant histiocytic neoplasm. (A) Coronal contrast-enhanced chest CT image and (B) T2-weighted fat-suppressed chest MR image reveal a large, heterogeneously enhancing mediastinal mass (arrows). The mass interfaces with the superior vena cava, left brachiocephalic vein, and pulmonary vasculature without airway compression. (C) Axial contrast-enhanced T1-weighted volumetric interpolated breath-hold examination findings show distortion of the right atrium (asterisk). (D) The tumor was intensely hypermetabolic (arrows) at coronal fused fluorine 18 fluorodeoxyglucose PET/MRI, with a maximum standardized uptake value of 14.
Primary malignant histiocytic neoplasms are rare tumors characterized by an accumulation of myeloid dendritic cell-derived invasive histiocytes and inflammatory infiltrate. The lineage and quality of inflammatory cells may independently suggest the diagnosis (1). Mitotic activity is prominent or atypical, and chromosomal gains or losses are frequent (2). Diagnosis is made by phenotypic and marker analysis (2). Clinical evidence of rapid tumor progression is necessary for confirmation (3). Primary malignant histiocytic neoplasms are exceedingly rare in children; more common histiocytoses in children include Langerhans cell histiocytosis and juvenile xanthogranuloma (1,4). Histiocytic disorders can affect any organ, with CT or MRI findings specific to location. Malignant histiocytic neoplasms are intensely fluorodeoxyglucose (FDG)-avid, underscoring the value of FDG PET/CT and PET/MRI for lesions undetectable at conventional CT or MRI (2,5). Oncogenic driver mutations of the RAS-RAF pathway have introduced novel precision therapy using RAF inhibitors (5).
Footnotes
Authors declared no funding for this work.
Disclosures of conflicts of interest: J.H. No relevant relationships. M.C.L. No relevant relationships. I.Y.C. No relevant relationships. A.C. No relevant relationships.
Keywords: Pediatrics, CT, PET/MR Imaging, Cardiac, Mediastinum, Oncology, Histiocytic, Mediastinal, Pericardial
References
- 1. Baraban E , Cooper K . Histiocytic and dendritic cell neoplasms of the mediastinum . Mediastinum 2020. ; 4 : 12 . [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Huynh KN , Nguyen BD . Histiocytosis and Neoplasms of Macrophage-Dendritic Cell Lineages: Multimodality Imaging with Emphasis on PET/CT . RadioGraphics 2021. ; 41 ( 2 ): 576 – 59 . [DOI] [PubMed] [Google Scholar]
- 3. Emile JF , Abla O , Fraitag S , et al. ; Histiocyte Society . Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages . Blood 2016. ; 127 ( 22 ): 2672 – 2681 . [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4. Eckstein OS , Picarsic J , Allen CE . Histiocytic Disorders of Childhood . Pediatr Rev 2022. ; 43 ( 10 ): 561 – 571 . [DOI] [PubMed] [Google Scholar]
- 5. Park H , Nishino M , Hornick JL , Jacobsen ED . Imaging of Histiocytosis in the Era of Genomic Medicine . RadioGraphics 2019. ; 39 ( 1 ): 95 – 114 . [DOI] [PMC free article] [PubMed] [Google Scholar]