Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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December 26, 2024
Solitary Plasmacytoma Petrous Apex
- Background:
- Plasmacytoma is characterized by the proliferation of monoclonal plasma cells, typically with absence or minimal marrow infiltration and without target organ lesion. There are 2 forms: solitary plasmacytoma of the bone and extramedullary plasmacytoma. Solitary plasmacytoma often affects the axial skeleton, and presentation in the petrous apex is a rare occurrence.
- Clinical Presentation:
- Patients typically present with a single painful bone lesion, pathologic fracture, or incidental finding.
- Key Diagnostic Features:
- CT shows expansile intraosseous soft tissue mass with lytic destruction of the petrous apex. On MRI, the lesion is isointense on T1-weighted imaging, iso- to hyperintense on T2-weighted imaging, and demonstrates moderate homogeneous enhancement.
- Differential Diagnosis:
- Metastasis: Adenocarcinoma is the most common (lung, breast, prostate, kidney, and melanoma). CT and MRI findings are variable and depend on the primary lesion.
- Chondrosarcoma: Typically originates off the midline from cartilaginous remnants of the petro-occipital fissure. CT may show chondroid matrix mineralization (rings and arcs). On MRI, is hypoisointense on T1-weighted imaging, hyperintense on T2-weighted imaging, and shows heterogeneous or uniform enhancement.
- Chordoma: Originates from embryonic remnants of the primitive notochord, typically midline in location. CT shows expansile soft tissue mass, normally hyperdense with lytic bone destruction. Tumor calcification may be seen in the chondroid variant. On MRI, can show variable signal on T1-weighted and hyperintensity on T2-weighted imaging, and shows heterogeneous enhancement.
- Paraganglioma: Arises from the jugular bulb or from Arnold or Jacobson nerves within the middle ear, may extend to involve the petrous apex. CT typically shows irregular erosion and a typical moth-eaten appearance of the left petrous apex with vivid enhancement. On MRI, can be heterogeneous on T1- and T2-weighted imaging, and shows vivid enhancement with flow voids, typically “salt and pepper” appearance.
- Endolymphatic sinus tumor: Usually located on the posterior petrosal surface, and most often associated with Von Hippel-Lindau disease. CT shows petrosal aggressive bone erosion in an infiltrative or "moth-eaten" pattern. On MRI, shows variable signal on T1-weighted and hyperintensity on T2-weighted imaging and vivid nodular enhancement.
- Management:
- Diagnosis is crucial as radiotherapy is the preferred treatment.
