Solitary plasmacytoma is a plasma cell neoplasm presenting as a single bone lesion, considered a localized form of multiple myeloma. In the chest wall, it most commonly affects the ribs and sternum. It is characterized by an expansile lytic lesion, homogeneous soft tissue component, and absence of sclerotic rim. Progression to multiple myeloma occurs in 50-70% of patients within 10-15 years, therefore systemic disease must be excluded with serum/urine protein electrophoresis (SPEP/UPEP), bone marrow biopsy, and whole skeletal survey. The mean age at diagnosis is 55-65 years, with a male-to-female ratio of 2:1.
Age Range
40-75
Peak Age
60
Gender
Male predominant
Prevalence
Rare
Solitary plasmacytoma originates from neoplastic proliferation of monoclonal plasma cells at a single location. These cells produce immunoglobulin similar to normal plasma cells, but with monoclonal (single-type) production — detected as M-protein in serum. Neoplastic plasma cells increase osteoclast activation through RANKL (receptor activator of nuclear factor kappa-B ligand) production and osteoprotegerin inhibition, leading to aggressive lytic bone destruction. The absence of sclerotic rim is explained by suppression of osteoblastic response (via DKK1 — Dickkopf-1 protein-mediated Wnt signaling pathway inhibition). The tumor grows expansively, thinning the bone cortex but usually maintaining an intact periosteal shell. The risk of progression to multiple myeloma is related to the presence of subclinical bone marrow involvement and circulating clonal plasma cells.
The most diagnostic imaging feature of plasmacytoma is the ABSENCE of reactive sclerotic rim while expansively thinning the bone cortex. This results from suppression of osteoblast activity via DKK1 protein. Aneurysmal bone cyst and giant cell tumor also create expansile lytic lesions but generally contain thin sclerotic rims. The combination of absent sclerotic rim + homogeneous soft tissue + middle-aged or older patient should strongly suggest plasmacytoma.
Well-defined expansile lytic lesion in rib or sternum lacking sclerotic rim. The cortex is thinned and may contain focal areas of destruction but the periosteal shell is generally intact. There is no matrix mineralization within the lesion. Thin residual bone trabeculae may create a 'soap bubble' appearance.
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An expansile lytic lesion measuring approximately _x_ cm is observed in the [Xth] rib/sternum without sclerotic rim; the cortex is thinned with focal areas of destruction.
The soft tissue component demonstrates prominent and homogeneous contrast enhancement. Plasma cell tumors have high vascularity and intense enhancement is characteristic. Necrosis areas are generally absent or minimal (except in large tumors). Surrounding soft tissue invasion is limited — the tumor usually remains well-defined.
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The lesion demonstrates homogeneous and prominent contrast enhancement on post-contrast series; no areas of necrosis are identified.
Homogeneous low to intermediate T1 signal intensity in the affected bone segment with loss of normal bone marrow fat signal. Signal may be iso- or slightly hypointense relative to muscle. Bone marrow infiltration margins are best evaluated on T1 sequence. Absence of additional infiltration in surrounding bone marrow supports the diagnosis of solitary plasmacytoma.
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Homogeneous low to intermediate signal intensity with loss of bone marrow fat signal is observed in the [Xth] rib/sternum on T1-weighted sequence, compatible with plasma cell infiltration.
Plasmacytoma shows intermediate signal intensity on T2-weighted sequences — there is no marked hyperintensity (unlike fluid-filled cysts). This intermediate signal reflects densely cellular tissue. Homogeneous signal distribution is characteristic. In large tumors, focal high signal areas may suggest hemorrhage or myxoid degeneration.
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The lesion shows homogeneous intermediate signal intensity on T2-weighted sequences without marked hyperintensity.
Prominent and homogeneous enhancement after gadolinium. The rich vascularity of plasma cell tumors leads to intense contrast uptake. The enhancement pattern is homogeneous — internal septations, necrosis, or non-enhancing areas are generally absent. The extraosseous component also demonstrates similar intense enhancement.
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The lesion demonstrates prominent and homogeneous enhancement on post-contrast T1 fat-suppressed sequences; no necrosis or non-enhancing areas are identified.
Moderate diffusion restriction is observed — less pronounced than Ewing sarcoma or lymphoma. ADC values are typically in the range of 0.8-1.2 × 10⁻³ mm²/s. Homogeneous restriction pattern reflects the uniform cellular composition of the tumor. DWI is also used in treatment response monitoring — ADC increases with successful treatment.
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The lesion shows moderate diffusion restriction on diffusion-weighted imaging (ADC: ~___ × 10⁻³ mm²/s).
Well-defined, expansile lytic lesion of the affected rib. The cortex is thinned but generally an intact periosteal shell is present. There is no sclerotic rim or periosteal reaction. No internal matrix mineralization is seen. Pathologic fracture may develop in large lesions.
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PA chest radiograph demonstrates a well-defined expansile lytic lesion of the [Xth] rib; no sclerotic rim or periosteal reaction is present.
The primary lesion shows moderate to high FDG uptake (SUVmax typically 3-10). Critically for solitary plasmacytoma diagnosis, there should be NO FDG-avid lesion in the remainder of the skeleton. PET-CT is more sensitive than conventional skeletal survey for detecting additional lesions and is the preferred modality for excluding multiple myeloma.
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The lesion at the level of the [Xth] rib demonstrates increased FDG uptake (SUVmax: ___). No additional FDG-avid lesion is detected in the remainder of the skeleton — compatible with solitary plasmacytoma.
Criteria
Most common form. Clonal plasma cell infiltration at a single bone location. Axial skeleton preference (vertebra > rib > sternum > pelvis). Less than 10% plasma cells in bone marrow biopsy. Progression to multiple myeloma in 50-70% of patients within 10-15 years.
Distinct Features
Single bone lesion, normal bone marrow biopsy, no systemic disease findings, low or absent M-protein
Criteria
Develops in extraosseous soft tissue. Most common in upper respiratory tract (nasopharynx, paranasal sinuses, oropharynx). Rare in chest wall — may originate from intercostal muscles or pleura. Lower risk of progression to multiple myeloma (10-30%). Good response to local radiotherapy.
Distinct Features
No bone involvement, soft tissue mass dominant, bone destruction only as secondary pressure erosion
Criteria
Solitary bone lesion present but clonal plasma cells detected by bone marrow flow cytometry or next-generation sequencing. Conventional bone marrow biopsy may be normal. This group has the highest risk of progression to multiple myeloma and requires closer follow-up.
Distinct Features
Single bone lesion but aberrant plasma cells on bone marrow flow cytometry, <10% on conventional biopsy
Distinguishing Feature
Multiple bone lesions (punch-out lytic lesions), >10% clonal plasma cells in bone marrow, high M-protein, anemia/hypercalcemia/renal failure (CRAB criteria). Multiple involvement on PET-CT or low-dose whole-body CT. Multiple myeloma MUST be excluded to diagnose solitary plasmacytoma.
Distinguishing Feature
Usually multiple bone lesions, known primary malignancy history. Isolated rib metastases are rare but possible (especially renal, thyroid, hepatocellular). Metastases tend to show more irregular destruction and heterogeneous enhancement. Periosteal reaction may be present (absent in plasmacytoma).
Distinguishing Feature
Expansile lytic lesion but usually with thin sclerotic rim. Low to intermediate T2 signal on MRI (due to hemosiderin deposition). Prominent enhancement. Age range 20-40 years. Very rare in rib — long bone epiphysis and vertebra preferred. Fluid-fluid levels (secondary aneurysmal bone cyst).
Distinguishing Feature
Expansile multiseptated cystic lesion. Fluid-fluid levels are pathognomonic (on MRI). Thin sclerotic rim usually present. Young age (10-30 years). Septal/peripheral enhancement on contrast series (not solid homogeneous enhancement). Fluid density internal structure on CT.
Urgency
moderateManagement
Definitive local radiotherapy (40-50 Gy) is the primary treatment modality for solitary plasmacytoma with local control rate >90%. Surgical resection is considered when radiotherapy is insufficient or there is risk of pathologic fracture. Systemic chemotherapy is NOT STANDARD in solitary plasmacytoma but may be controversially applied in high-risk patients (large tumor, persistent M-protein). Long-term follow-up is mandatory due to risk of progression to multiple myeloma after treatment.Biopsy
NeededFollow-up
Mandatory workup at diagnosis: SPEP, UPEP, free light chain ratio, bone marrow biopsy, whole-body PET-CT or low-dose whole-body CT. Post-treatment: follow-up every 3-6 months for first 3 years, then every 6-12 months. Follow-up includes: SPEP/UPEP (M-protein monitoring), CBC (anemia), calcium, creatinine, annual whole-body PET-CT/low-dose CT (new lesion screening). M-protein increase, new bone lesion, or CRAB symptoms suggest progression to multiple myeloma. Follow-up should continue lifelong.Solitary plasmacytoma is a plasma cell neoplasm with good prognosis with local treatment but requiring lifelong follow-up due to the risk of progression to multiple myeloma. The most critical step at diagnosis is excluding systemic disease (multiple myeloma) — SPEP/UPEP, bone marrow biopsy, and whole skeletal imaging (PET-CT preferred) are mandatory for this purpose. Biopsy planning should be based on imaging findings, and CT-guided percutaneous biopsy is usually sufficient.
When solitary plasmacytoma is diagnosed, multiple myeloma must be excluded (whole-body PET-CT or MRI, bone marrow biopsy, serum/urine protein electrophoresis). Localized radiotherapy (40-50 Gy) is the gold standard in treatment, achieving >80% local control rate. 50-70% of patients progress to multiple myeloma within 10 years — long-term follow-up is mandatory. Surgical resection should be considered for large lesions or pathologic fracture risk.