PMC8592761_01
(a, b) MRI images demonstrate heterogeneously enhancing 2.7 cm extraconal mass lesion (yellow arrows), inferior to right globe and displacing it superolaterally.
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fig1
Magnetic resonance imaging (MRI) demonstrated a heterogeneously enhancing 2.7 x 1.8 x 3.0 cm mass, extraconal and isointense to the extraocular muscles, inferior to the right globe and displacing it superolaterally (Figure 1).
Histologic images from pretreatment incisional biopsy of the right orbital mass. H&E stains demonstrate a hypercellular proliferation of rhabdomyoblasts, showing a spectrum from primitive to differentiating forms, the latter of which feature elongated eosinophilic cytoplasm (strap cells) ((a) 100x magnification; (b) 400x magnification). Immunohistochemical stains demonstrate frequent myogenin staining of moderate intensity ((d) 100x magnification), strong myoD1 expression ((e) 100x magnification), and a high Ki67 proliferation index ((e) 40x magnification) in the rhabdomyoblasts.
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fig2
An incisional biopsy demonstrated a hypercellular proliferation of primitive small round blue and spindled cells, featuring numerous strap cells and fascicular architecture (Figure 2).
Histologic images from the posttreatment incisional biopsy of the right orbital mass. H&E stains demonstrate a variably cellular proliferation of terminally differentiated rhabdomyoblasts with eccentric nuclei and dense eosinophilic cytoplasm ((a) 100x magnification), with relatively few scattered foci showing primitive rhabdomyoblasts in the background ((b) 400x magnification). Immunohistochemical stains demonstrate scattered myogenin expression ((c) 100x magnification), infrequent myoD1 expression ((d) 100x magnification), and a low Ki67 proliferation index ((e) 100x magnification), all of which are markedly decreased in comparison to expression patterns from the pretreatment biopsy (Figure 2).
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fig3
An incisional biopsy at this time point demonstrated sheets of mature rhabdoid cells (90%), in a sclerotic background, with only limited areas of primitive rhabdomyoblasts (10%) (Figure 3).