Contributed by Elizabeth M. Sagatys1, MD, Jane L. Messina2, MD and Amyn M. Rojiani3, MD, PhD
1. University of South Florida College of Medicine Department of Pathology, Tampa, Florida
2. University of South Florida College of Medicine Department of Pathology and
Dermatopathologist at Moffitt Cancer Center and Research Institute, Tampa Florida
3. University of South Florida College of Medicine, Department of Pathology and
Neuropathologist at Moffitt Cancer Center and Research Institute, Tampa Florida
A 55-year-old man presented for a routine preoperative chest x-ray in preparation for a knee replacement. Imaging revealed an extrapleural paraspinal mass in the region of T8. Fine needle aspiration of the mass was interpreted as melanoma. Neurologic examination was unremarkable. Total body skin examination failed to reveal any suspicious pigmented lesions. The mass was in close connection with the exiting T8 nerve root and somewhat adherent to the sympathetic chain. The mass was removed within an intact capsule. Immunohistochemical staining and electron microscopy of the resected specimen revealed a malignant melanotic schwannoma. The features of melanotic schwannoma, both benign and malignant variants, and their distinction from melanoma are discussed.
A 55-year-old man presented to an outside institution for a routine preoperative chest x-ray in preparation for a knee replacement. The chest x-ray demonstrated a mass in the right lower lobe. Additional imaging with computerized tomography and a Positron Emission Tomography scan demonstrated a 1.5 cm extrapleural paraspinal mass in the region of T8, which also had mild increase in glucose uptake. Transthoracic fine needle aspirate was performed.
The patient reported no history of melanoma and no change in any moles or other pigmented lesions on his skin. He was asymptomatic, with no reports of shortness of breath, chest pain, neurologic symptoms, night sweats, weight loss, nausea/vomiting, bone pain or weakness. Medical history was significant for hepatitis C and atrial fibrillation. Both parents had histories of colonic carcinoma. There was no other history of cancer in the family.
Physical examination was unremarkable with no point tenderness over the thoracic spine and no sensory deficits. Neurologic examination was unremarkable. Total body skin examination failed to reveal any suspicious pigmented lesions.
An MRI of the thoracic spine with and without contrast demonstrated a well-defined mass in the right paraspinal soft tissue at T8 level (Figure 1). The mass was 2.2 x 2.0 cm and demonstrated fairly homogenous contrast enhancement with extension into the adjacent right neural foramen, suggesting tumoral extension into this region. No cord compression was noted.
The patient elected to have the lesion surgically removed. The surgeon noted the mass was in close connection with the exiting T8 nerve root and somewhat adherent to the sympathetic chain. The mass was separated from the pleura and other surrounding structures and removed within an intact capsule.
Fine Needle Aspirate:
Papanicolaou-stained smears and cellblock from the CT guided biopsy contained fragments of cohesive epithelioid tumor cells with mild to moderate nuclear atypia and prominent cherry red nucleoli (Figure 2). Brown pigment seen in both, the tumor cells and the macrophages was confirmed to be melanin by a positive Fontana-Masson stain and a negative Perl's stain for hemosiderin. The tumor cells showed strong positivity for S100 and HMB-45. These cells were negative for immunohistochemical markers Mart-1, desmin, GFAP and pan-keratin.
Resection of Sepcimen::
The specimen was an encapsulated, ovoid, tan-white to brown mass, 2.5 x 1.7 x 1.0 cm. Cut sections revealed a dark-brown nodule, 1.8 x 1.5 x 0.9 cm. A representative section submitted for frozen section analysis revealed benign appearing peripheral nerve sheath components consistent with melanotic schwannoma.
Permanent sections displayed multiple growth patterns (Figures 3 and 4). The central portion of the nodule was large epithelioid cells, prominent red nucleoli, intranuclear inclusions and intracellular brown pigment. The lesion had a high mitotic rate (4/10 HPF). The peripheral portion of the lesion was predominantly spindle cells with features of benign peripheral nerve sheath tumor and peripheral nerve. Within the benign appearing portion of the lesion were multiple scattered pigmented cells and clusters of bland epithelioid cells. The atypical tumor cells were strongly immunoreactive for S100 and pan-melanoma marker (Figures 5 and 6) and focally reactive for Melan A and HMB45. The adjacent large and small peripheral nerve segments were also immunoreactive for S100. The lesional cells and the adjacent nerve and nerve sheath segments were also immunoreactive for CD57 (Leu 7) and collagen type IV (Figures 7 and 8). Electron microscopy demonstrated melanosomes in various stages of maturation, intercellular junctions and a well defined basal lamina (Figures 9 and 10).