1. Introduction
Plasmacytomas of the skull base are rare manifestations of plasma cell neoplasms, representing a small fraction of all head and neck tumors and an even smaller subset among plasma cell dyscrasias [ 1 , 2 ]. These tumors can present either as solitary lesions, termed solitary bone plasmacytoma (SBP) or extramedullary plasmacytoma (EMP) when in soft tissues, or as secondary lesions in the context of systemic multiple myeloma (MM) [ 1 , 3 ]. Epidemiologically, skull base plasmacytomas are most commonly diagnosed in middle-aged to older adults, with a mean age around 54 years, though cases in younger patients have been documented and are considered unusual [ 4 , 5 ]. The majority of skull base plasmacytomas originate from middle cranial fossa structures such as the clivus, sphenoid bone, and petrous apex, while a lesser subset of lesions occasionally arise from bones of the face [ 2 , 3 ].
Pathophysiologically, plasmacytomas are characterized by the monoclonal proliferation of plasma cells, which secrete immunoglobulins and may infiltrate bone or soft tissue [ 1 ]. The distinction between solitary plasmacytoma and multiple myeloma is critical. According to the International Myeloma Working Group (IMWG) criteria, a solitary plasmacytoma requires a biopsy-proven single clonal lesion of bone or soft tissue, a normal skeletal survey and axial MRI (or CT) of the spine and pelvis apart from the primary lesion, and the absence of end-organ damage attributable to a clonal plasma-cell disorder. A variant termed solitary plasmacytoma with minimal marrow involvement permits clonal marrow plasma cells below 10%. By contrast, multiple myeloma is defined by clonal bone marrow plasma cells of at least 10% (or a biopsy-proven plasmacytoma) plus one or more myeloma-defining events, including CRAB features, or biomarkers of malignancy [ 6 ]. Skull base plasmacytomas, particularly those arising from the clivus, sphenoid, or petrous apex, carry a high risk of progression to multiple myeloma, with reported rates of conversion exceeding 50% within two years of diagnosis ( Figure 1 ) [ 1 , 3 , 7 ]. Genetic alterations, including deletions in p53 , 13q14, and translocations involving immunoglobulin heavy chain loci, have been implicated in disease progression, though the molecular mechanisms remain incompletely understood [ 8 ].
Clinical presentation is typically dominated by symptoms related to the mass effect (such as headache, visual disturbances, and vomiting) and cranial nerve involvement, with the abducens nerve most frequently affected [ 1 , 3 ]. Diagnostic evaluation involves imaging, particularly MRI and CT, followed by a histopathologic confirmation with immunohistochemical staining for plasma cell markers and light chain restriction [ 3 ]. A comprehensive systemic workup is essential to rule out underlying or concurrent multiple myeloma [ 1 , 3 ].
Given the rarity of skull base plasmacytomas, the limited number of reported cases, and their high risk of progression to multiple myeloma, a comprehensive synthesis of the existing literature is essential to better understand epidemiology, pathophysiology, clinical presentation, and management. This systematic review aims to report evidence-based practices, improve the diagnostic accuracy, and optimize the outcomes for affected patients, while also providing an update on the existing literature and highlighting gaps that warrant further research [ 2 ].
2. Materials and Methods
2.1. Literature Search
A systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines ( Supplementary Files S1 and S2 ). The review was not prospectively registered in PROSPERO or another protocol registry, which we acknowledge as a limitation. PubMed, EMBASE, Web of Science, and Cochrane were searched from database inception to February 2025, operating the Boolean full-text search [(“plasmacytoma” OR “extramedullary plasmacytoma” OR “solitary bone plasmacytoma”) AND (“skull base” OR “clivus” OR “sphenoid” OR “petrous apex”)]. The same controlled-vocabulary and free-text terms were applied to each database, adapting the syntax to each platform: in PubMed, the strategy combined MeSH terms (“Plasmacytoma”[Mesh] and “Skull Base”[Mesh]) with the title/abstract keywords above; EMBASE used the corresponding Emtree terms with .tw/.mp field tags; and Web of Science and Cochrane (CENTRAL) used the same keyword strings within Topic/Title–Abstract–Keyword fields. No date, language, or document-type filters were applied at the database level; eligibility restrictions were applied only at screening. Reference lists of included studies and of relevant prior reviews were hand-searched, but a formal grey-literature search (e.g., trial registries, theses, and preprints) was not performed. Conference abstracts and proceedings were excluded a priori because they typically lack the individual patient-level clinical, treatment, and follow-up detail required for extraction in this analysis and are frequently superseded by subsequent full-text publications, raising the risk of duplicate counting. Studies were exported to Rayyan and duplicates were removed. To further mitigate the risk of duplicate inclusion of the same patient across overlapping case reports and case series, records were cross-checked for matching author groups, institutions, patient age and sex, tumor location, and treatment timeline, and apparent duplicates were resolved by retaining the most complete report.
2.2. Study Selection
Inclusion and exclusion criteria were defined as follows. Articles were included if they fulfilled the following criteria: (1) they report adult patients with histologically confirmed diagnosis of plasmacytoma and radiologically confirmed skull base location; (2) they include individual patient data including details of clinical factors, treatment, outcome, and follow-up; and (3) they were written in English. Studies were excluded if they fulfilled the. following criteria: (1) they were autopsy reports, animal studies, or studies focusing on imaging characteristics, genetics, or histopathology only; (2) they were conference abstracts, literature reviews, meta-analyses, systematic reviews, perspectives, or editorials; (3) they lacked adequate clinical data; (4) they were non-English or non-peer-reviewed sources; and (5) they were reports in the pediatric population, as plasmacytomas in this population differ meaningfully in biological behavior, treatment protocols, and diagnostic considerations, which would introduce clinical heterogeneity into the analysis.
Two independent reviewers (G.T. and T.K.B.) screened all titles and abstracts from the initial systematic search and assessed the full texts of articles that met the inclusion criteria. Two different reviewers (F.C.O. and K.B.) settled disagreements. Eligible papers were included. References of included studies were also screened to identify additional pertinent studies.
2.3. Data Extraction
Two reviewers (G.T. and T.K.B.) extracted data from each article, which was confirmed independently by two additional reviewers (F.C.O. and K.B.). Extracted data included authors, year published, sample size, age, gender, presenting symptoms and their duration, comorbidities, physical exam findings, radiological findings, surgical intervention and extent of resection, histopathological findings, adjuvant therapy received, time to recurrence, time of last follow-up with clinical status, and survival.
2.4. Data Analysis and Quality Assessment
The primary variables of interest were clinical characteristics, management strategies used, and treatment outcomes for patients with SBPs. For each study, two independent authors (F.C.O and T.K.B.) assessed the level of evidence using the 2011 Oxford Centre For Evidence-Based Medicine guidelines and the risk of bias by applying the Joanna Briggs Institute checklists for case reports and case series [ 9 , 10 , 11 ]. Meta-analysis was precluded because most included studies had levels IV–V of evidence (except for one level III with exhaustive individual patient data) and hazard ratios could not be deduced.
2.5. Statistical Analysis
Microsoft Excel (Microsoft Corporation, Redmond, WA, USA) was used for all data collection and analysis for central tendency and distribution. Continuous variables are summarized as medians with ranges and categorical variables are summarized as frequencies with percentages.
Pooled individual patient data allowed for univariate analysis using Chi-square or Fisher’s exact test and log-rank analysis plotted as Kaplan–Meier survival curves. Multivariate analysis was done using binary logistic regression. Statistical analysis was done using RStudio v2024.04.2. The multivariable model was specified as binary logistic regression predicting vital status (alive vs. deceased) at last reported follow-up rather than a Cox model, as individual-level time-to-event data were unavailable across the heterogeneous source studies. Given the limited number of outcome events relative to candidate predictors, the conventional events-per-variable threshold of ~10 was not met, and estimates should be interpreted as exploratory and hypothesis-generating rather than confirmatory. Categorical predictors in which all events fell within a single subgroup produced complete separation and are reported as non-estimable in the results.
3. Results
3.1. Study Inclusion
Figure 2 illustrates the flow diagram of the literature search. The search strategy yielded 707 studies (PubMed: 256, EMBASE: 164, Web of Science: 287, Cochrane: 0), of which 92 were included upon the pre-specified study inclusion criteria: 18 were case series [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] and 74 were case reports [ 1 , 3 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ], with IV, and V levels of evidence, respectively ( Table 1 ).
3.2. Patient Demographics and Clinical Presentation
A total of 118 patients with skull base plasmacytomas were included. The median age was 56 years (range, 19–81 years), and 65 patients (55%) were male. Among 85 patients with available data, the median duration of symptoms prior to diagnosis was 2 months (range, 0.07–66 months). A personal history of multiple myeloma was present in 29 patients (24.6%) out of 118 with available data, while 89 (75.4%) had no such history ( Table 2 ).
The most common presenting symptoms were visual disturbances, reported in 78 patients (66.1%), and headache in 64 (54.2%), followed by motor disturbances in 18 (15.3%), and palpable mass or swelling in 15 (12.7%). Auditory disturbances (tinnitus, and hypoacusis) and dizziness/vertigo each occurred in 13 patients (11%). Sensory disturbances and ataxia/gait disturbance were each seen in 10 patients (8.5%). Less frequent symptoms included mechanical pain ( n = 8, 6.8%), cognitive dysfunction ( n = 7, 5.9%), dysphagia ( n = 6, 5.1%), nausea/vomiting ( n = 5, 4.2%), nasal discomfort ( n = 5, 4.2%), speech problems ( n = 3, 2.5%), and several non-specific symptoms each reported in a single case (0.8%).
Cranial nerve involvement was documented in 67 patients. The abducens nerve was most commonly affected ( n = 44, 65.7%), followed by the trigeminal ( n = 19, 28.4%), oculomotor ( n = 11, 16.4%), facial ( n = 7, 10.4%), optic ( n = 6, 9%), trochlear ( n = 6, 9%), vestibulocochlear ( n = 4, 6%), hypoglossal ( n = 3, 4.5%), and vagus ( n = 1, 1.5%) nerves.
3.3. Clinical Workup
Initial imaging modality was reported for 113 patients. MRI was the most frequently used ( n = 92, 81.4%), with lesions typically showing hypointense ( n = 12, 10.6%) or isointense ( n = 31, 27.4%) on T1-weighted imaging and isointense ( n = 15, 13.2%) or hyperintense ( n = 16, 14.2%) on T2. MRI-based contrast enhancement was reported for 67 patients with most having a homogeneous enhancement ( n = 50, 42.4%). CT was performed in 69 patients (61.1%), X-ray in 19 (16.8%), PET scan in 9 (7.9%), and MRA in 3 (2.6%) ( Table 3 ).
The tumor location was reported for all 118 patients. The middle cranial fossa was the most common site ( n = 57, 48.3%), followed by the posterior fossa ( n = 40, 33.9%), a tumor involving both the middle and posterior fossa ( n = 9, 7.6%), a non-specified skull base location ( n = 7, 5.9%), a tumor involving both the anterior and middle fossae ( n = 3, 2.5%), and the anterior fossa ( n = 2, 1.7%).
Local invasion was documented in nearby structures as shown in 89 of 107 patients with available data (83.2%), particularly to the adjacent bone ( n = 29, 32.6%), cavernous sinus ( n = 26, 29.2%), and sphenoid sinus ( n = 22, 24.7%). A histopathologic examination was available for all patients. All lesions were confirmed plasmacytoma, with inflammatory features noted in 25 (21%), lymphocytic infiltrate in 13 (11%), necrosis in 4 (3.4%), vasculitis in 3 (2.5%), and calcification in 3 (2.5%).
3.4. Management and Outcomes
Neoadjuvant therapy was not administered or not reported in 112 patients (94.9%). Chemotherapy was used as neoadjuvant therapy in 3 patients (2.5%), radiotherapy in 2 (1.7%), and combined chemoradiotherapy in 1 (0.8%).
The initial treatment consisted of surgery in 75 patients (63.6%), radiotherapy alone in 25 (21.2%), combined radiotherapy and chemotherapy in 15 (12.7%), and chemotherapy alone in 3 (2.5%). Those undergoing conventional radiotherapy received a median dose of 40 Gy (24–60 Gy), while data for stereotactic modality was limited. Among surgical cases ( n = 75), subtotal resection (STR) was achieved in 35 (46.6%), gross total resection (GTR) in 27 (36%), and the extent of resection was not reported in 13 (17.3%). Intraoperative complications were rare, with no complications occurring in 72 cases (96%), hemorrhage in 2 (2.6%), and pituitary lesion in 1 (1.3%) ( Table 4 ).
Adjuvant therapy was not specified or not used in 46 patients (38.9%). Conventional radiotherapy was used in 40 (33.8%), chemotherapy in 17 (14.4%), combined radiotherapy and chemotherapy in 14 (11.8%), and stereotactic radiosurgery in 1 (0.8%). Median dose among those receiving radiotherapy was 45 Gy (13–54 Gy), and fractioning was inconsistently reported. Post-treatment imaging was performed in 76 of 89 patients (85.4%), with 32 (42.1%) showing residual disease.
During follow-up, from the 89 patients who did not have a personal history of MM, the development of systemic disease occurred in 23 (19.5%), 55 (46.6%) had negative tests, and, for 11 (9.3%) patients, the source studies did not report progression or screening for MM. A single recurrence occurred in 22 (18.6%) patients and multiple recurrences in 1 (0.8%). The median time to last follow-up was 12 months (range, 0.35–120 months) with reports of having a resolution of symptoms in 45 patients (38.1%), an improvement in 31 (26.2%), worsening in 23 (19.5%), and symptom stability in 19 (16.1%). At the final status assessment ( n = 118), 96 patients (81.4%) were alive and 22 (18.6%) had died.
3.5. Statistical Analysis
On univariate analysis, associations between the status at last follow-up, recurrence status, and symptomatic control, with initial treatment modalities were assessed but no statistical differences were found ( p values of 0.74, 0.4, and 0.66, respectively). Local invasion was not associated with the extent of resection ( p = 0.13). Survival probability ( Figure 3 ) was not statistically significant when comparing the initial treatment modality (surgical or non-surgical, p = 0.15), but a statistically significant difference ( p < 0.01) was found when comparing the MM status.
Binary logistic regression identified MM history as the only statistically significant predictor of survival status at last follow-up. Patients who never developed MM had significantly higher odds of survival compared to those diagnosed with MM postoperatively (OR = 10.14, 95% CI: 1.63–63.04, p = 0.013). The tumor location, presence of local invasion, and initial treatment modality were not significantly associated with survival outcomes ( Table 5 ).
4. Discussion
4.1. Patient Demographics and Epidemiological Insights
Na’ara et al. (2016) conducted a meta-analysis of 47 patients with skull base plasmacytomas, providing foundational insights into the demographics, clinical presentation, management strategies, and outcomes associated with this rare tumor [ 2 ]. Our expanded cohort of 118 patients builds upon this existing literature, offering a broader demographic and clinical spectrum. Rather than positioning this work as practice-changing, we frame its contribution as a descriptive, contemporary update to the existing literature and as a hypothesis-generating resource for a rare disease that cannot be studied prospectively at single centers. Relative to the foundational meta-analysis by Na’ara et al., the present synthesis adds value in several concrete respects. First, it expands the pooled sample size roughly two-and-a-half-fold (118 versus 47 patients), improving the precision with which clinical patterns can be described. Second, it documents a clear temporal shift in management toward operative intervention (surgery in 63.6% of our cohort versus 46.8% previously), reflecting the evolution of endoscopic and open skull base techniques. Third, it stratifies the multiple myeloma status by its timing relative to the skull base lesion (pre-existing versus subsequently developed, and preoperative versus postoperative diagnosis), allowing the prognostic weight of systemic disease to be examined more granularly than in prior work. Fourth, it expands the characterization of cranial-nerve involvement and patterns of local invasion, including structures and deficits not detailed in the earlier report. We acknowledge that these contributions are incremental and descriptive rather than definitive, and the associations reported here should be regarded as hypotheses to be tested in future prospective, multicenter collaborations.
Beyond describing clinical patterns in a larger cohort, this synthesis contributes a prognostic refinement. When the multiple myeloma status was stratified by its temporal relationship to the skull base lesion, patients who never developed myeloma had markedly higher odds of survival than those diagnosed with myeloma postoperatively (OR = 10.14, 95% CI: 1.63–63.04, p = 0.013), whereas a preoperative myeloma diagnosis conferred no significant survival difference relative to postoperative diagnosis (OR = 0.697, p = 0.622). This dissociation indicates that it is the presence of systemic disease, rather than its timing relative to local treatment, that governs prognosis, a distinction that reframes myeloma progression, rather than the local intervention chosen, as the dominant survival determinant and identifies myeloma conversion as the principal actionable endpoint for surveillance. Coupled with the documented shift toward operative management in the absence of a corresponding survival gain, these observations yield two clinically relevant implications for an ultra-rare disease: the escalation of surgical aggressiveness should be weighed against its unproven survival benefit, and structured long-term hematologic surveillance for myeloma conversion should be prioritized.
Both studies report a comparable median age of approximately 56 years; however, our cohort exhibits a slightly wider age range (19–81 years) compared to the 2016 cohort (28–85 years). While the previous study documented a male predominance of 59%, our analysis reveals a more balanced sex distribution, with males representing 55% of cases. These findings suggest a consistency in age-related epidemiology but indicate potential demographic shifts or subtle sampling variability in sex distribution [ 2 ].
4.2. Differential Pathologies
The diagnosis of skull base plasmacytoma remains a significant clinical challenge due to its substantial overlap in presentation and imaging characteristics with other skull base neoplasms, particularly chordomas and meningiomas [ 2 ]. Due to the local anatomy, these lesions commonly involve similar structures and present with similar symptoms, most commonly visual disturbances due to cranial nerve involvement [ 102 , 103 ]. However, due to differing pathology and disease progression, accurate diagnosis is critical for appropriate management, planning, and prognostic understanding. Chordomas are locally aggressive and have high recurrence rates [ 102 ]. Conversely, meningiomas are usually low-grade lesions with indolent growth and behavior [ 104 ].
In terms of patient demographics, skull base meningiomas have a female prevalence (2:1) while plasmacytomas and chordomas are more prevalent in males [ 102 , 105 ]. Other differentiating factors from imaging findings and immunohistochemistry (IHC) are instrumental in distinguishing plasmacytomas from these other neoplasms. On MRI imaging, plasmacytomas usually appear isointense on T1-weighted images and isointense to hyperintense on T2-weighted images, with a marked homogeneous contrast enhancement. Furthermore, clival destruction is frequently seen on computed tomography (CT) [ 106 ]. In comparison, chordomas are more likely to show a hypointense appearance on T1-weighted imaging with a heterogeneous enhancement [ 105 ]. Meningiomas appear isointense on both T1- and T2-weighted MRI, with cases commonly having an enhancing dural “tail” [ 105 ]. However, the presence of imaging findings mimicking a dural “tail” have been reported in cases of plasmacytoma, so this finding alone is not pathognomonic [ 106 ].
IHC findings often provide a key differentiating factor in the diagnoses of plasmacytomas of the skull base. They typically show light chain restriction and stain positive for CD138, CD38, and CD56. Notably, CD138 positivity identifies plasma cells, while CD56 is a marker that is usually negative in normal plasma cells [ 106 ]. Epithelial membrane antigen (EMA) may be positive in some cases of plasmacytomas, but this finding is more likely to be seen in skull base chordomas and meningiomas [ 107 , 108 , 109 ]. Chordomas additionally show high rates of cytokeratin and brachyury positivity on immunohistochemistry [ 110 ]. While an overlap in IHC findings is present, the presence of plasma cell markers is a specific feature that can confirm a diagnosis of plasmacytoma compared to other skull base lesions.
4.3. Tumor Location and Clinical Presentation
In both our cohort and the 2016 meta-analysis by Na’ara et al., visual disturbances emerged as the most common presenting symptom, reflecting the cranial nerve involvement associated with the lesion proximity to the optic pathway, cranial nerves, and related structures [ 2 ]. Although different location categorizations were used, the 2016 study reported that most of the included lesions were in the sphenoclival area (59.5%) or petrous apex (10.6%), which broadly aligns with our study, where most lesions were localized to the middle cranial fossa or posterior fossa. Anterior fossa involvement was rare in both studies, reported at 8.5% (4/47) in the 2016 report [ 2 ] and 4.2% (5/118) in our report.
In addition to visual symptoms, other neurologic deficits such as sensory and motor disturbances, along with hearing loss, were observed at lower rates. Abducens and oculomotor nerve involvement were prevalent in both reports, consistent with tumor encroachment on the parasellar and prepontine regions. Notably, our cohort exhibited higher rates of trigeminal (28.4%) and facial nerve (10.4%) involvement, with no included lesions impacting the olfactory nerve. In contrast, the 2016 report did not include any mention of trigeminal or facial nerve involvement but did have 10 cases (21.2%) of olfactory nerve involvement. Both studies reported cases of vestibulocochlear nerve involvement, however, at lower comparative rates, with symptoms manifesting as hearing loss, vertigo, and ataxia [ 2 ]. These patterns suggest a shared clinical phenotype centered on cranial neuropathies, while also highlighting potential anatomical and methodological variations that may influence the detection and reporting of specific nerve deficits.
4.4. Treatment Modalities and Clinical Outcomes
A notable divergence between our findings and those of Na’ara et al. (2016) lies in the evolving treatment landscape [ 2 ]. In the earlier cohort, the majority of patients (53%) received non-surgical management—radiotherapy alone (27.6%), chemotherapy alone (4.2%), or combined chemoradiotherapy (21.2%) [ 2 ]—with surgical resection performed in 47% of cases. In contrast, our study demonstrates a clear shift toward operative management, with 63.6% of patients undergoing surgical intervention. This trend likely reflects the advances in skull base surgical techniques and a growing inclination toward resection in selected patients.
Among those managed surgically, gross total resection (GTR) remained relatively infrequent in both cohorts, achieved in 36% of our cases and 45% in the 2016 study [ 2 ], underscoring the technical challenges posed by the proximity of these lesions to critical neurovascular structures. The high prevalence of local invasion observed in our cohort (83.2% of patients with available data) is a key contributor to this challenge. The most frequently invaded structures were adjacent bone (32.6%), the cavernous sinus (29.2%), and the sphenoid sinus (24.7%), which represent critical anatomical barriers to complete the resection at the skull base. Despite this, univariate analysis did not identify a statistically significant association between the presence of local invasion and extent of resection ( p = 0.13), suggesting that other factors like tumor volume, approach selection, and surgeon experience may more directly determine the resectability in individual cases. Adjuvant radiotherapy remained a mainstay in both studies, regardless of the extent of the resection, reinforcing its role in multimodal treatment strategies.
Regarding the radiotherapy modality, most patients in our cohort who received radiation were treated with conventional fractionated radiotherapy, while only two patients received stereotactic radiosurgery as the initial modality and one as adjuvant therapy. Although emerging reports suggest that stereotactic modalities may offer effective local control with favorable toxicity profiles in selected skull base plasmacytoma cases [ 56 , 74 , 75 ], the predominance of conventional radiotherapy in our dataset precluded a meaningful comparative analysis between radiation modalities.
Despite the differences in the therapeutic approaches, the survival outcomes were broadly comparable. At a median follow-up of 12 months, 81.4% of patients in our cohort were alive, with 64.3% demonstrating symptomatic improvement or resolution. This is similar to findings from the prior report which reported a two-year survival of 78% and a five-year survival of 59% [ 2 ]. Furthermore, their multivariate analysis revealed no statistically significant association between surgical intervention or the extent of resection on the overall survival rate [ 2 ]. This finding correlates with the data seen in our report, with survival rates of our cohort being similar despite a higher proportion of patients treated with surgical resection.
Collectively, these observations suggest that, while surgical resection may offer symptomatic relief and local control in selected cases, its impact on long-term survival remains uncertain. This highlights the urgent need for prospective, ideally multicenter, studies to rigorously evaluate the comparative efficacy of surgical versus non-surgical modalities, and to define evidence-based guidelines for managing skull base plasmacytomas. Future research should also incorporate standardized functional outcome measures and long-term quality-of-life assessments, which are currently underreported. In addition, the integration of molecular profiling and imaging biomarkers may help stratify patients by recurrence risk and guide individualized therapeutic strategies.
A biological rationale helps explain why a higher proportion of surgical resection in our cohort did not translate into a measurable survival advantage. Plasmacytomas are composed of clonal plasma cells that are intrinsically radiosensitive, and definitive radiotherapy alone achieves durable local control in a large majority of solitary plasmacytomas, with most series reporting local control exceeding 80–90% at moderate doses on the order of 40–50 Gy [ 110 ]. Because radiotherapy reliably eradicates or controls the local lesion, cytoreductive surgery offers a limited incremental benefit for local control and has not been shown to improve overall survival; in this disease, long-term prognosis is instead driven chiefly by the progression to systemic multiple myeloma rather than by local tumor management [ 110 , 111 , 112 , 113 ].
Within this framework, the principal roles of surgery could be viewed as to establish a tissue diagnosis or, more importantly, to relieve the mass effect or neural compression. This paradigm could explain the comparable survival observed across treatment strategies in both our cohort and the earlier meta-analysis.
4.5. Multiple Myeloma History and Its Prognostic Significance
The relationship between MM status and survival emerged as the most clinically significant finding in this analysis. Among the 89 patients without a prior history of MM at presentation, 23 (19.5%) developed systemic disease after treatment, 55 (46.6%) remained disease-free at follow-up, and the MM screening status was not reported in 11 (9.3%). An additional 29 patients (24.6%) presented with a pre-existing MM diagnosis. Importantly, the timing of the MM diagnosis relative to the skull base plasmacytoma (preoperative or postoperative) carried distinct prognostic implications.
A Kaplan–Meier analysis demonstrated a statistically significant difference in overall survival when stratifying by MM status ( p < 0.01). On multivariate binary logistic regression, MM history was the only independent predictor of survival status at last follow-up. Patients who never developed MM had 10-fold higher odds of survival compared to those with a postoperative MM diagnosis (OR = 10.14, 95% CI: 1.63–63.04, p = 0.013). In contrast, patients with a preoperative MM diagnosis did not demonstrate a statistically significant difference in survival compared to the postoperative MM group (OR = 0.697, p = 0.622), suggesting that, once systemic disease is established, its impact on prognosis may be independent of whether it preceded or followed treatment. These findings are consistent with the broader literature on solitary plasmacytoma, where MM progression is the primary determinant of long-term prognosis, with reported conversion rates of 50–60% within the first two years of diagnosis for solitary bone plasmacytoma [ 1 , 7 ]. The tumor location, presence of local invasion, and initial treatment modality were not independently associated with survival outcomes ( Table 5 ), reinforcing that systemic disease burden, rather than local tumor characteristics, drives prognosis in this population. These findings underscore the critical importance of rigorous long-term surveillance for MM conversion in all patients treated for skull base plasmacytoma, and the need for a standardized prospective reporting of the timing of MM progression in future studies.
4.6. Limitations
This systematic review has several limitations. The included studies were predominantly case reports and small case series, which are susceptible to reporting, selection, and publication bias. The publication bias is likely substantial and directional: unusual presentations, favorable responses, and successfully managed cases are preferentially reported, so the pooled frequencies and survival estimates are probably biased toward optimism. The overall sample size, while the largest pooled cohort to date, limits the statistical power and contributes to the wide confidence intervals in the logistic regression model.
Outcome reporting was inconsistent across studies, limiting the interpretation of long-term results. Radiotherapy parameters were incompletely documented, as fractionation schemes were frequently omitted, precluding dose-response analysis. The near-exclusive use of conventional radiotherapy also precluded meaningful comparison of radiation modalities.
The timing of MM progression was inconsistently reported; authors frequently documented MM at follow-up without specifying the interval from treatment. All post-treatment MM cases were, therefore, grouped together, which may obscure the differences between early and late progressors. Functional outcomes were rarely reported using validated instruments, limiting the assessment of the treatment impact on recovery and quality of life.
Diagnostic criteria distinguishing solitary plasmacytoma, extramedullary plasmacytoma, and myeloma-associated disease were not uniformly applied across source studies, many of which predate current IMWG definitions. The pooled cohort is, therefore, biologically heterogeneous, and pooled estimates should be interpreted as describing a mixed plasma cell neoplasm population rather than a uniformly defined solitary plasmacytoma cohort.
Finally, the higher surgical proportion in our cohort alongside survival comparable to historical non-surgical series should not be interpreted as evidence of therapeutic equivalence or superiority. These are non-randomized retrospective data subject to confounding by indication, and no causal claim regarding any treatment modality is warranted.
5. Conclusions
This systematic review provides the largest pooled analysis to date of skull base plasmacytomas, elucidating their clinical presentation, anatomical distribution, treatment modalities, and outcomes. Our expanded cohort identified shifts in management, particularly increased surgical intervention. Despite this trend, survival outcomes remain comparable to prior data, a pattern that, while not establishing causation in these non-randomized data, is consistent with the limited additional survival benefit from resection alone. Stratifying myeloma status by its timing relative to the lesion further clarified that systemic disease burden, not the timing of its diagnosis or the local treatment chosen, is the dominant survival determinant, establishing myeloma conversion as the principal actionable endpoint for long-term surveillance. The rarity of these tumors and the predominance of low-level evidence underscore the need for prospective, multicenter studies with standardized reporting. Future research should prioritize molecular characterization and long-term functional outcomes to inform individualized, evidence-based management strategies.
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Supplementary Materials
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cancers18152495/s1 , Supplementary File S1: Full Electronic Search Strategy. Supplementary File S2: PRISMA 2020 checklist. Reference [ 114 ] is cited in the Supplementary Materials.
Author Contributions
All authors contributed substantially to the manuscript. All authors have read and agreed to the published version of the manuscript.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
All data generated or analyzed during this study are included in this article. Further inquiries may be directed to the corresponding author.
Conflicts of Interest
The authors declare no conflicts of interest.
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