In a 30-year-old female with a stable 3 cm lytic lesion of the right posterior fossa skull adjacent to the foramen magnum and vertebral artery, presenting with neck pain, dizziness, nausea and visual changes but no systemic symptoms, is the lesion most likely a benign cystic bone lesion rather than malignancy, and should the next step be laboratory evaluation for plasma-cell dyscrasia before considering biopsy?

Management of Stable Lytic Skull Lesion in Young Adult

In this 30-year-old woman with a stable 3 cm posterior fossa lytic lesion and no systemic symptoms, the lesion is overwhelmingly likely benign—most probably an aneurysmal bone cyst—and the next step should be laboratory evaluation for plasma cell dyscrasia (serum protein electrophoresis, immunofixation, free light chains) to exclude the very unlikely possibility of solitary plasmacytoma, followed by neurosurgical consultation for potential biopsy given her symptomatic presentation and the lesion's proximity to critical structures. 1, 2

Age-Stratified Risk Assessment

• At age 30, primary bone sarcomas and benign aggressive lesions (aneurysmal bone cyst, giant cell tumor) are statistically more likely than metastatic disease or multiple myeloma. 1, 2
• In patients under 40 years, an aggressive symptomatic bone lesion carries significant risk of being a primary bone tumor rather than metastasis. 1
• Multiple myeloma typically presents in patients over 40 years and is exceedingly rare in this age group, though solitary plasmacytoma remains a consideration. 1

Clinical Features Favoring Benign Diagnosis

• The two-year duration with stable lesion size on serial imaging strongly argues against malignancy, as primary bone sarcomas and metastatic lesions typically demonstrate progressive growth. 2, 3
• Absence of constitutional symptoms (fever, night sweats, unintentional weight loss), normal performance status (Karnofsky 100), and lack of other bone pain make systemic malignancy extremely unlikely. 1, 4
• The imaging characteristics—well-defined lytic lesion without mass effect, edema, or vascular compromise—are consistent with benign cystic pathology. 1, 3, 5

Aneurysmal Bone Cyst as Leading Diagnosis

• Aneurysmal bone cysts (ABC) are benign, expansile, fluid-filled lesions that commonly affect young adults and can occur in the skull, though cranial involvement is exceptional. 3, 5
• ABCs characteristically present as lytic, expansile lesions with fluid levels on MRI and can cause local symptoms from mass effect without systemic manifestations. 3, 5
• The posterior fossa location, young age, chronic symptoms, and stable imaging over time all support ABC as the most likely diagnosis. 3, 5

Laboratory Evaluation Strategy

Complete the following blood work to exclude plasma cell dyscrasia with very high confidence: 1

• Serum protein electrophoresis (SPEP) and immunofixation

• Serum free light chains (kappa and lambda)

• Quantitative immunoglobulins (IgG, IgA, IgM)

• Complete blood count, comprehensive metabolic panel including calcium and creatinine

• Alkaline phosphatase and lactate dehydrogenase

• If these laboratories are normal, the probability of multiple myeloma is essentially zero, as symptomatic myeloma requires both M-protein ≥3 g/dL or bone marrow plasma cells ≥10% plus end-organ damage. 1

• A solitary plasmacytoma cannot be definitively excluded without tissue diagnosis, but remains unlikely given the patient's age and clinical presentation. 1

Imaging Adequacy and PET Scan Consideration

• The current MRI and CT imaging is adequate for characterization; PET scan is NOT recommended at this time unless new concerning symptoms develop (progressive weight loss, fever, night sweats, new bone pain, lymphadenopathy). 1
• Additional skeletal imaging (bone scan or whole-body MRI) is not indicated in the absence of other bone pain or systemic symptoms. 1

Biopsy Decision Algorithm

Given the symptomatic presentation and critical anatomic location, neurosurgical consultation for biopsy versus excision is reasonable after laboratory results return, using the following framework: 1, 2

Indications favoring biopsy/excision:

• Persistent symptoms (neck pain, dizziness, nausea, visual changes) potentially attributable to the lesion 1, 3
• Proximity to foramen magnum and vertebral artery creates risk if lesion progresses 3, 5
• Young mother with small child who requires diagnostic certainty 1
• Inability to completely exclude solitary plasmacytoma or other pathology without tissue 1

Indications favoring continued observation:

• Stable size over nearly two years of imaging surveillance 2, 3
• Imaging characteristics highly consistent with benign process 1, 3
• Biopsy in this location carries surgical risk given proximity to vertebral artery and brainstem 1, 3

Critical Referral Requirements

• If biopsy is pursued, it MUST be performed at a bone sarcoma reference center or by a neurosurgeon experienced in skull base pathology, as inappropriate biopsy technique can compromise subsequent treatment. 1, 2
• Core needle biopsy under imaging guidance is preferred over open biopsy when feasible, though the posterior fossa location may necessitate open approach. 1, 2
• The biopsy tract must be planned for potential en bloc resection if malignancy is discovered. 1, 2

Common Pitfalls to Avoid

• Do not assume benignity based solely on stable imaging; tissue diagnosis may still be warranted given symptomatic presentation. 1, 2
• Do not perform biopsy at a non-specialized center, as bone lesions are frequently difficult to diagnose even by experienced pathologists. 1, 2
• Do not delay neurosurgical consultation if symptoms progress or new neurologic deficits develop. 1, 4
• A negative myeloma workup does not exclude solitary plasmacytoma, which requires tissue diagnosis for definitive exclusion. 1

Follow-Up Recommendations

• Review laboratory results in 2-3 weeks as planned 1
• If laboratories are reassuring, discuss observation versus biopsy with neurosurgery, weighing symptom burden against surgical risk 1, 2, 3
• If observation is chosen, repeat MRI in 6 months to confirm continued stability 2, 3
• Counsel patient on red flag symptoms requiring immediate evaluation: severe headache, new neurologic deficits, visual changes, or worsening neck pain 1, 4