An 8-year-old boy presented with a polypoid translucent mass that could be easily seen in his upper oropharynx. On endoscopy the mass was seen to be originating from the maxillary antrum and extending from it on a long, attenuated stalk. A snare excision was performed and the specimen was submitted to pathology.
Microscopically the surface consisted of variably hyperplastic and attenuated squamous, intermediate and respiratory mucosa. Features of a Scheiderian papilloma were not present. The stroma contained scattered variably atypical, often greatly enlarged cells. Because of concern for a sarcoma, the case was referred to us in consultation. Several H&E images of the lesion are shown below.
What is your diagnosis?
The stroma is loose and somewhat edematous and constains mild acute and chronic inflammation. Scattered throughout the stroma but never forming more hypercellular aggregates, are greatly enlarged stellate stromal cells. These cells exhibit both nuclear and cytoplasmic enlargement with accordingly nearly unchanged nuclear to cytoplasmic ratios. Mitotic figures are not noted. Immunohistochemical stains for cytokeratins, muscle specific actin, smooth muscle actin, and desmin are negative. This is an example of an antrochoanal polyp with marked, but completely benign, stromal atypia.
Longstanding stromal-epithelial polyps at a wide variety of anatomic sites, including vaginal polyps, inflammatory nasal polyps, fibrous papules of the nose, and antrochoanal polyps are well known to often show considerable stromal atypia, perhaps relating to persistent trauma. Antrochoanal polyps, unlike more typical inflammatory nasal polyps, are prone to occur in younger children and in this population confusion of this benign change with a botryoid sarcoma can be a devastating pitfall. Fortunately the distinction is easy to make if one is aware of this lesion and, if necessary, confirms the absence of rhabdomyogenous differentation with appropriate immunohistochemical stains.
Unlike the botryoid variant of embryonal rhabdomyosarcoma, antrochoanal polyps with stromal atypia lack the hypercellular "cambium layer" typical of the former tumors. The atypical stromal cells are also considerably larger than the cells of embryonal rhabdomyosarcoma and lack more than rare mitotic figures, which should be typical in appearance. Some caution with immunohistochemistry is warranted, as these cells may show some minimal myofibroblastic differentiation (lacking in this case), but they will lack staining for skeletal muscle markers. Most commonly they stain only for vimentin.