Contributed by Nicole Delaney, MD and Raja Seethala, MD
Department Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA 15213
A male in his 60s presented with a slowly growing, progressively enlarging expansile lytic mass in the petrous area of his left temporal bone present for several years on radiologic imaging (Figure 1).
The patient's past medical history is significant for resection of a left parapharyngeal space mass diagnosed as acinic cell carcinoma more than a decade ago which was also treated with radiation therapy. He subsequently had locoregional disease recurrence about five years after the initial resection treated with surgery and radiation therapy (Figure 2). He is otherwise in good health with no other history of malignancy.
The mass was resected via endoscopic endonasal approach for diagnosis and treatment. A representative sample of the mass was sent for intraoperative consultation. Frozen section examination showed occasional nests of eosinophilic cells, including scattered cells with nuclear pleomorphism, in a background of fibrous connective tissue (Figure 3).
The diagnosis was deferred (atypical cellular proliferation, favor malignant, rule out radiation atypia) and additional tissue was requested if possible for permanent examination.
Formalin-fixed paraffin-embedded material demonstrates two areas within the mass with distinctive morphology (Figure 4).
In some areas, the mass shows a more low-grade mixed microcystic and solid appearance with relatively bland cytonuclear features (Figure 5). In other areas, the mass shows a high-grade appearance consisting of sheets of highly atypical dyscohesive single cells with marked nuclear pleomorphism and rare foci of osteoid-like material (Figure 6).
A few foci within the mass show that areas with low-grade and high-grade morphology are closely associated (Figure 7).
Immunohistochemistry demonstrates that the high-grade areas are focally positive for cytokeratins (pankeratin and CAM5.2) while the low-grade areas are diffusely positive (Figure 8). A DOG-1 immunostain is also focally positive in the high-grade areas while the low-grade areas show diffuse positive membranous-type staining for DOG-1 (Figure 9). The high-grade areas show an increased proliferative index compared to the low-grade areas by Ki-67/MIB-1 immunohistochemistry (Figure 10) while a p53 immunostain shows extreme positivity in the high-grade areas compared to the low-grade areas (Figure 11).