Primary Thoracic Myxoid Variant of Extrarenal Rhabdoid Tumor in Childhood

Abstract

Primary extrarenal rhabdoid tumors (RT) are now recognized as a specific entity in pediatric oncological pathology practice. We present an unusual case of a small cell myxoid variant of a thoracic RT in an infant and highlight the importance of recent molecular developments in the diagnosis of these tumors. An 8-month-old child presented with a short history of cough and shortness of breath. Imaging demonstrated a large mass occupying the majority of the thoracic cavity on the right side. A percutaneous needle biopsy of the mass showed fragments of tissue composed of malignant tumor with a predominant "small ovoid cell" phenotype and extensive myxoid change, with small nests and islands of tumor cells; occasional cells demonstrated open vesicular nuclei, prominent nucleoli, and eosinophilic cytoplasmic inclusions. Immunohistochemical staining revealed focal strong cytoplasmic positivity for cytokeratin, focal strong paranuclear cytoplasmic vimentin positivity, and INI1 staining showed normal nuclear positivity in control tissues but was negative in tumor cell nuclei. Electron microscopy demonstrated characteristic paranuclear whorls of intermediate filaments confirming the diagnosis of extrarenal malignant RT. The diagnosis of malignant rhabdoid tumor may be difficult, particularly in cases, such as the present, with a predominant small-cell myxoid phenotype. The characteristic expression patterns of cytokeratin and vimentin provide strong clues to the diagnosis, and the use of INI1 antibody now makes definitive diagnosis possible even on needle core biopsies.

Soft tissue myoepithelial carcinoma with rhabdoid‐like features andEWSR1rearrangement: Fine needle aspiration cytology with histologic correlation

“…In the present case, the neoplastic cells showed prominent nucleoli with abundant cytoplasm and rhabdoid‐like appearance, making the diagnosis of soft tissue malignant rhabdoid tumor (MRT) likely on cytologic smear. MRT cytology often reveals moderate to high cellularity; the three most common features are eccentrically placed nuclei, prominent nucleoli, and large tumor cells . However, on cytology MRT can also reveal a predominant small cell population and the differential diagnosis with other small round cell tumors is a challenge …”

“…The cytological differential diagnosis of tumors with rhabdoid features depends mainly on the location of the neoplasm . In addition, the list of tumors with rhabdoid morphology has increased in recent years .…”

“…In pediatric, and less frequently in adult patients, with soft tissue tumors displaying evident rhabdoid morphology, an extrarenal malignant rhabdoid tumor is the most probable diagnosis. Furthermore, the cytologic features of extrarenal malignant rhabdoid tumor are similar to the renal or brain counterpart . The differential diagnosis should include all soft tissue tumors that exhibit rhabdoid morphology (epithelioid rhabdomyosarcoma, Ewing sarcoma/PNET, neuroblastoma, desmoplastic small round cell tumor, epithelioid sarcoma proximal type, MEC, extraskeletal myxoid chondrosarcoma, rhabdoid pancreatic/gastrointestinal metastatic carcinoma, rhabdoid melanoma)…”

Immunohistochemistry as potential diagnostic pitfall in the most common solid tumors of children and adolescents

“…3A and B) (Fowler et al, 2006;Alaggio et al, 2009) and variable CD99 expression ( Fig. 3C) (Fanburg-Smith et al, 1998;Alaggio et al, 2009;Machado et al, 2010).…”

“…Although its morphology is typical, we have already emphasized that a small round cell component may be variably represented throughout the tumor (Fowler et al, 2006;Alaggio et al, 2009). Accordingly, differential diagnostic problems between a blastemal-dominant Wilms' tumor and a MRT arise when dealing with bioptic material from tumor renal masses, which contain exclusively/predominantly a small, round cell component.…”