Introduction
Temporal bone plasmacytoma is an exceedingly rare form of plasmacytoma, a monoclonal proliferation of plasma cells that predominantly occurs in the medullary cavities of bones or in soft tissues. Plasmacytoma is primarily categorized into solitary bone plasmacytoma (SBP), extramedullary plasmacytoma (EMP), and multiple myeloma (MM). Of these, temporal bone involvement is particularly uncommon, with solitary bone plasmacytoma presenting as a localized neoplasm in the temporal bone's marrow, often involving the petrous part of the temporal bone, skull base, and occasionally extending into surrounding structures [ 1 ].
The clinical presentation typically includes symptoms such as unilateral hearing loss, tinnitus, pain, and in more advanced cases, cranial nerve deficits, due to the mass effect and the tumor’s proximity to critical neural structures. The initial diagnostic challenge lies in the non-specific nature of these symptoms, which can mimic other conditions like cholesteatomas or middle ear infections. Advanced imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI) are crucial for detecting the extent of bone involvement and soft tissue extension. On CT scans, plasmacytomas often show a destructive, lytic bone lesion, while MRI demonstrates characteristic enhancement and mass effect [ 2 ].
The management of temporal bone plasmacytoma primarily involves localized radiotherapy (RT), which remains the cornerstone of treatment due to its high local control rates of 83-96%. Typically, RT is administered at doses of 40-50 Gy. Surgical intervention, limited to biopsy or subtotal excision, is considered only in cases with neurological compromise or for diagnostic clarification. Chemotherapy is generally not indicated unless there is progression toward multiple myeloma (MM). Given the risk of SBP evolving into MM, patients require lifelong follow-up, including periodic imaging and laboratory investigations to monitor for recurrence or systemic spread. Despite a favorable prognosis with RT, vigilant long-term surveillance is essential due to the possibility of disease progression, particularly within the first 3 to 5 years, when the risk of dissemination is highest [ 3 ].
Case presentation
We present the case of a 65-year-old female patient with a medical history of hypertension, managed with a combination of antihypertensive medications, and a facial trauma sustained 20 years ago. The patient was referred to our institution due to the progressive enlargement of a right temporal mass, which had been gradually increasing in size over the past 10 months ( Fig. 1 ). This mass was accompanied by a gradual deterioration in her overall health status.
Upon physical examination, a firm, non-pulsatile, and fixed mass was palpated in the deep planes of the right temporal region. It was tender to palpation but did not exhibit any pulsation. The remainder of the physical examination did not reveal any significant abnormalities.
Initial laboratory investigations included a complete blood count (CBC), which indicated anemia with a hemoglobin level of 9 g/dL. Inflammatory markers were elevated, with a C-reactive protein (CRP) level of 40 mg/L and an erythrocyte sedimentation rate (ESR) of 30 mm/h. Additionally, protein electrophoresis showed evidence of monoclonal protein production. No other significant findings were noted in the remainder of the biological workup.
Cranial and facial computed tomography demonstrated an ill-defined soft-tissue mass in the right anterior temporal and peri-orbital region, associated with focal osteolysis of the temporal bone, including erosion of the lateral orbital wall ( Fig. 2 ).
Subsequent brain magnetic resonance imaging revealed a tumor-like lesion involving the anterior temporal region with irregular, poorly defined margins. The lesion demonstrated intermediate signal intensity on T2-weighted images and slight hyperintensity relative to adjacent muscle on T1-weighted images, with marked and heterogeneous enhancement following contrast administration. Diffusion-weighted imaging showed signal characteristics suggestive of diffusion restriction. The lesion measured approximately 27 × 16 mm and was associated with involvement of the lateral orbital wall ( Fig. 3 ).
Additional imaging sequences were not available; however, the performed contrast-enhanced CT and MRI examinations were sufficient to characterize the lesion and assess its local extent.
Given the clinical presentation and radiological findings, a multidisciplinary tumor board discussion recommended performing a biopsy of the temporal mass. Histopathological and immunohistochemical analyses confirmed the diagnosis of plasmacytoma ( Fig. 4 , Fig. 5 , Fig. 6 ).
Considering the tumor's anatomical location in the right temporal and peri-orbital region, along with the histological confirmation of plasmacytoma with monoclonal Kappa light chain restriction, a decision was made to proceed with radiotherapy. The patient received a total radiation dose exceeding 40 Gy, which was delivered in daily fractions over a period of 6 weeks. This therapeutic regimen aimed to achieve local control of the tumor and minimize the risk of further progression, particularly given the aggressive nature of the plasmacytoma and its involvement with surrounding structures, including the osseous tissue of the orbit.
The patient was placed under regular follow-up, with clinical evaluations scheduled every 4 months during the first 2 years post-treatment. As of the time of writing this report, no signs of local recurrence have been observed.
Discussion
Plasmacytomas are rare, monoclonal neoplasms originating from terminally differentiated B lymphocytes known as plasma cells. They belong to a spectrum of plasma cell dyscrasias that includes solitary bone plasmacytoma (SBP), extramedullary plasmacytoma (EMP), and multiple myeloma (MM). SBP refers to a single osseous lesion composed of clonal plasma cells without systemic marrow involvement or paraproteinemia, whereas EMP arises from soft tissues, commonly of the upper aerodigestive tract. Plasmacytoma of the temporal bone is an exceptional entity within this spectrum. The temporal bone’s marrow-rich petrous portion offers a niche for neoplastic plasma cell proliferation, yet only a handful of cases have been documented. Understanding this tumor’s biology and clinical course is essential, as it often precedes or evolves into systemic multiple myeloma [ 4 ].
Solitary bone plasmacytomas represent less than 5% of all malignant plasma cell tumors. The temporal bone accounts for a minute fraction of these cases, with fewer than 2 dozen well-documented reports in the English literature. The mean age at presentation is between 45 and 60 years, with a male predominance of approximately 3:1. Although most SBPs occur in the vertebral column, pelvis, and femur, involvement of the skull base and temporal bone remains exceptionally rare. Symptoms usually appear after local destruction and expansion due to the bone’s compact nature and proximity to neurovascular structures. Approximately 50% of SBP cases evolve into multiple myeloma within 3-5 years, underscoring the need for vigilant, lifelong surveillance [ 5 ].
The pathogenesis of plasmacytoma involves malignant transformation of a post-germinal center B-cell clone that secretes a single immunoglobulin subtype. This clonal expansion leads to localized osteolytic activity mediated by cytokines such as IL-6, RANKL, and macrophage inhibitory factor, which promote osteoclast activation and bone resorption. The temporal bone, particularly its petrous and mastoid portions, contains marrow spaces that may harbor precursor B-cells prone to neoplastic transformation. Histologically, these tumors consist of sheets of mature or atypical plasma cells with eccentric nuclei and perinuclear halos, often accompanied by amyloid deposits. Immunohistochemical staining demonstrates monoclonality, typically with CD138 positivity and restriction for κ or λ light chains. The biological behavior of temporal bone plasmacytoma parallels that of skeletal SBP but may exhibit more aggressive local infiltration due to the confined anatomic space [ 6 ].
The diagnosis of temporal bone plasmacytoma requires a comprehensive multidisciplinary approach combining radiologic, histopathologic, and laboratory investigations. High-resolution temporal bone CT typically demonstrates a well-circumscribed, osteolytic, and expansile lesion involving the mastoid or petrous bone, often extending into adjacent structures such as the middle ear, jugular bulb, or sigmoid sinus. MRI provides superior soft-tissue definition, showing an isointense to hyperintense signal on T1- and T2-weighted sequences with homogeneous gadolinium enhancement, and is indispensable for assessing dural or cranial nerve involvement. To confirm disease unifocality, whole-body MRI or 18F-FDG PET/CT is strongly recommended, as these modalities can exclude occult lesions elsewhere in the skeleton or soft tissue—an essential step before classifying the tumor as a solitary bone plasmacytoma (SBP) [ 7 ] .
Histopathologic confirmation is mandatory and represents the diagnostic gold standard. Biopsy specimens reveal sheets of mature or atypical plasma cells with eccentric nuclei and perinuclear clearing. Immunohistochemistry demonstrates plasma cell markers (CD138, CD38) and restriction to a single light chain (κ or λ), confirming monoclonality. Occasionally, amyloid deposition or atypical mitoses may be noted. Flow cytometry and FISH testing can further identify cytogenetic abnormalities, although these are primarily prognostic rather than diagnostic. The absence of polymorphous inflammatory cells or polyclonal light-chain expression distinguishes plasmacytoma from reactive plasma cell granuloma and other neoplastic mimics [ 8 ].
Laboratory and marrow studies are crucial to exclude multiple myeloma. Serum and urine electrophoresis with immunofixation, free light-chain assays, and bone marrow biopsy must be performed. The IMWG diagnostic criteria define SBP by: (1) histologic evidence of clonal plasma cells in a single bone lesion; (2) < 10% plasma cell infiltration in bone marrow; (3) absence of additional lesions on whole-body imaging; and (4) lack of CRAB features—hypercalcemia, renal impairment, anemia, or multiple lytic lesions. When these conditions are met, the diagnosis of solitary plasmacytoma of the temporal bone is established. This distinction is critical, as it guides treatment strategy and long-term surveillance, given the potential for systemic progression in up to half of patients within several years.
Differential diagnosis of a temporal bone plasmacytoma encompasses a variety of entities presenting with lytic lesions or soft-tissue masses. Chief considerations include metastatic carcinoma, cholesteatoma, glomus jugulare tumors, meningioma, lymphoma, and inflammatory pseudotumor (plasma cell granuloma). Radiologically, glomus tumors exhibit intense vascularity and salt-and-pepper appearance, whereas plasmacytomas demonstrate homogeneous enhancement and bone erosion without hypervascular blush. Plasma cell granuloma can mimic plasmacytoma histologically but lacks cytologic atypia and monoclonal immunoglobulin expression. Hence, immunohistochemistry and electrophoresis remain decisive in distinguishing plasmacytoma from benign plasma cell infiltrates or other malignancies [ 9 ].
The management of temporal bone plasmacytoma is primarily based on definitive local radiotherapy, which remains the standard of care due to the tumor’s marked radiosensitivity. Current guidelines recommend a total dose of 40-50 Gy delivered in 1.8-2 Gy daily fractions to the gross tumor volume with a 1.5-2 cm margin. Radiotherapy achieves local control rates exceeding 85-90% and provides durable remission in most cases. For lesions greater than 5 cm or those abutting critical neurovascular structures, intensity-modulated radiation therapy (IMRT) is preferred to optimize dose conformity and spare adjacent organs, such as the cochlea and brainstem. In temporal bone disease, radiation fields must encompass potential microscopic spread along marrow spaces and skull-base foramina. Pre-treatment dental and otologic evaluation is recommended to reduce late complications, particularly in skull-base irradiation [ 10 ].
Surgical management plays an adjunctive but often critical role in both diagnosis and treatment. Biopsy or subtotal excision is generally indicated to confirm histopathology, alleviate mass effect, and obtain decompression in cases of facial nerve palsy, brainstem compression, or venous sinus involvement. However, complete surgical resection is rarely feasible because of the anatomic complexity of the temporal bone and the risk of cranial neuropathies. When performed, surgery should always be followed by adjuvant radiotherapy to minimize local recurrence. In extensive or infiltrative lesions, a combined neurosurgical–otologic approach using an infratemporal or translabyrinthine corridor can provide safe tumor access while preserving critical structures [ 11 ].
Systemic therapy is not routinely indicated for solitary lesions but may be considered in patients with minimal bone marrow involvement (< 10%), persistent monoclonal protein, or early biochemical progression. In such settings, bortezomib- or lenalidomide-based chemotherapy may delay transformation to multiple myeloma. Long-term surveillance is essential for all patients, consisting of serial clinical evaluations, serum and urine electrophoresis, free light-chain monitoring, and whole-body imaging every 6-12 months. Approximately 30-50% of cases may eventually evolve into systemic disease over several years. Early detection of recurrence or systemic progression allows prompt initiation of anti-myeloma therapy following standard myeloma protocols. Therefore, management of temporal bone plasmacytoma requires a multidisciplinary strategy, combining radiation oncology, otology, hematology, and radiology expertise to achieve both optimal local control and long-term systemic surveillance [ 12 ].
The clinical evolution of temporal bone plasmacytoma largely depends on both local disease control and the risk of systemic transformation. Following appropriate radiotherapy, most patients experience durable local remission, with recurrence rates reported below 10%. Post-treatment imaging typically shows progressive ossification or sclerosis of the lytic cavity within months, indicating favorable response. However, due to the anatomical complexity of the temporal bone and its proximity to the cranial nerves and dural sinuses, local recurrence can manifest through subtle neurologic deficits such as hearing loss, vertigo, or facial nerve weakness. These signs warrant prompt MRI reassessment, as early relapse confined to the original site may still be amenable to re-irradiation or limited salvage surgery [ 13 ].
Despite high rates of local control, systemic progression remains the most significant prognostic concern. Approximately 30-50% of solitary bone plasmacytomas eventually evolve into multiple myeloma, typically within 3-5 years of initial diagnosis. Predictors of systemic transformation include persistence or reappearance of serum monoclonal protein after radiotherapy, abnormal serum free light-chain ratio, minimal bone marrow infiltration (≥ 5% clonal plasma cells), and tumor size ≥ 5 cm at presentation. Patients with negative post-treatment M-protein and normal FLC ratio have significantly better outcomes, with a 10-year myeloma-free survival exceeding 80%. Regular follow-up every 3-6 months for the first 5 years, then annually, is strongly recommended. Each visit should include physical examination, serum electrophoresis, FLC assay, and imaging when clinically indicated [ 14 ].
Overall prognosis for solitary plasmacytoma of the temporal bone is favorable when diagnosed early and managed appropriately. The median overall survival exceeds 10 years, and many patients remain disease-free for decades. However, given the non-negligible risk of systemic dissemination, long-term surveillance is mandatory. Transition to multiple myeloma necessitates systemic therapy following standard protocols, including proteasome inhibitors and immunomodulatory agents. Early recognition of progression substantially improves outcomes. In summary, while temporal bone plasmacytoma carries an excellent local prognosis under optimal management, it remains a potential harbinger of systemic plasma cell dyscrasia, demanding vigilant multidisciplinary follow-up throughout the patient’s lifetime [ 15 ].
Conclusion
Temporal bone plasmacytoma is an exceptionally rare form of plasma cell neoplasm that requires a high index of clinical suspicion, meticulous diagnostic evaluation, and multidisciplinary management. Accurate diagnosis relies on advanced imaging, histopathologic confirmation of clonal plasma cells, and exclusion of systemic disease in accordance with IMWG criteria. Radiotherapy remains the mainstay of treatment, achieving high local control rates and long-term remission, while surgery is reserved for biopsy or decompression in selected cases. Although the prognosis is generally favorable, with many patients achieving durable local control, approximately one-third to one-half may eventually progress to multiple myeloma, most commonly within the first few years after diagnosis. Consequently, lifelong clinical, radiologic, and hematologic surveillance is essential. Early recognition and coordinated care between otologic, hematologic, and radiation oncology teams are paramount to optimizing outcomes and ensuring prompt detection of systemic transformation.
Patient consent
The patient has provided informed consent for the publication of this case report.
Footnotes
Acknowledgments: The authors extend their gratitude to the otorhinolaryngology department team at the university hospital for their management and availability. This study did not receive any specific funding from public, commercial, or non-profit funding agencies.
Competing Interests: The authors have declared that no competing interests.
Contributor Information
Mohammed Amine Rabhi, Email: mohammed.amine.rabhi@gmail.com.
Saad Bouchlarhem, Email: bouchlarhemsaad@gmail.com.
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