PMC9771651_01
Pre- and postsurgical imaging. (a) A/P shoulder X-ray that was unremarkable. (b) Coronal short tau inversion recovery (STIR) MRI imaging showing an enhancing mass with heterogeneity (red arrow). (c) Precontrast nonfat sat T1-weighted MRI imaging showing the mass to be uniformly hypointense. (d) T1 axial fat-suppression postcontrast MRI showing heterogenous enhancing mass. (e) Image taken during US-guided biopsy showing an enlarged mass (red arrow) arising from nerve (red stars) most consistent for a PNST. (f) Postsurgical PET/CT scan showing some residual FDG signal in the postsurgical bed of the right arm (red arrow) and progression of metastatic PTC (mediastinal adenopathy, right upper paravertebral/subpleural nodule, para-aortic nodule, right medial upper lung nodule, and left upper lobe solid mass).
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These symptoms prompted diagnostic imaging (Figure 1). Right humerus MRI revealed a 3.5 x 2.3 x 1.8 cm solid mass in the neurovascular bundle of the medial arm which was hypointense on T1 and hyperintense on T2 with postcontrast enhancement (Figures 1(b)-1(d), red arrows). He was referred to the orthopaedic oncology clinic for further evaluation, where an ultrasound-guided biopsy was performed (Figure 1(e)). Regions of the neoplasm exhibited loose, myxoid regions with bland spindled cells which were positive for CD34 in a characteristic "thumbprint" pattern of neurofibroma (Figure 2, B1 and D2). Other foci featured an increased cellularity of spindled cells arranged in fascicles and palisades, which were negative for CD34, compatible with schwannoma (Figure 2, B3 and D1). Due to these histopathological and NGS findings, a full body PET/CT scan was performed to determine metastatic burden (Figure 1(f)).
Histopathology of hybrid neurofibroma/schwannoma component. Low-magnification images ((a) 40x and (b) 100x) identify the neurofibroma (A1/B1), schwannoma (B3), and metastatic carcinoma (A2/B2). Immunohistochemistry for SOX10 (c) is positive within the NF and schwannoma portions, but negative in the carcinoma portions (C2). CD34 (d) is negative within the schwannoma component (D3) and exhibits the so called "thumbprint" appearance in the NF component (D1).
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Histologic examination showed a benign peripheral nerve sheath tumor (PNST) which exhibited a hybrid of morphologies (Figures 2(a) and 2(b)), with features of a schwannoma as well as a neurofibroma with metastatic PTC deposits. Regions of the neoplasm exhibited loose, myxoid regions with bland spindled cells which were positive for CD34 in a characteristic "thumbprint" pattern of neurofibroma (Figure 2, B1 and D2). Other foci featured an increased cellularity of spindled cells arranged in fascicles and palisades, which were negative for CD34, compatible with schwannoma (Figure 2, B3 and D1). The lesional cells from both components of the PNST were immunoreactive for both S100 and Sox10 (Figure 2(c)). TTF1 were both positive in the glandular cells, which were negative for Sox10 (Figure 2, C2). Thus, the glandular component was most consistent with a metastatic PTC. The final diagnosis rendered was mixed PNST (4.5 cm) harboring metastatic PTC (1.8 cm) (Figures 2(a) and 2(b)).
Histopathology of PTC component. Lower magnification images ((a) 40x and (b) 100x) and higher magnification images ((c) 200x and (d) 400x) highlight the metastatic cells arranged in glands. These cells exhibit classical nuclear features of papillary thyroid carcinoma including nuclear grooves and intranuclear pseudoinclusions ((d) circled). Immunohistochemistry for AE1/AE3 (e) and PAX8 (f) are positive within the glands, confirmatory for metastatic PTC.
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Other foci featured an increased cellularity of spindled cells arranged in fascicles and palisades, which were negative for CD34, compatible with schwannoma (Figure 2, B3 and D1). These glandular cells exhibited atypical morphology with rare cells bearing classical nuclear features of papillary thyroid carcinoma (PTC), including powdery chromatin, nuclear grooves, and prominent intranuclear cytoplasmic inclusions (Figures 3(a)-3(d)).