What is the most likely diagnosis for a patient with a lytic lesion in the right occipital skull base?

Most Likely Diagnosis: Chordoma

For a lytic lesion in the right occipital skull base, chordoma is the most likely diagnosis, particularly in an adult patient, as this tumor characteristically arises from notochordal remnants along the axial skeleton with the skull base (specifically the clivus and occipital bone) being one of the two most common locations. 1

Key Diagnostic Considerations

Primary Differential for Skull Base Lytic Lesions

Chordoma should be at the top of your differential for several critical reasons:

• Location specificity: Chordomas arise from notochordal remnants and preferentially occur at the skull base (particularly clivus/occipital region) and sacrum 1
• Age distribution: Median age is 60 years, though skull base presentations can affect younger populations including children and adolescents 1
• Imaging characteristics: These are locally invasive, destructive lesions that create lytic bone destruction 1
• Clinical behavior: Chordoma is a low-grade but locally aggressive malignancy with approximately 30% metastatic potential, though prognosis relates more to local aggressiveness than metastases 1

Other Important Considerations in the Differential

While chordoma is most likely, you must also consider:

• Metastatic disease: Always in the differential for lytic skull base lesions, particularly in older patients with known primary malignancies 2
• Plasmacytoma: Can present as a solitary lytic skull base lesion and may mimic other tumors on imaging 3
• Ewing's sarcoma: Particularly in pediatric/adolescent patients presenting with lytic occipital bone lesions 4
• Meningioma: Though typically not purely lytic, skull base meningiomas can cause bone erosion and should be considered with associated soft tissue mass 5

Diagnostic Workup Algorithm

Imaging Protocol

1. MRI is the best modality for local staging of skull base chordomas 1
2. CT scan should be used to better characterize bone destruction and in cases of diagnostic doubt 1
3. Obtain thin-section imaging through the skull base to define involvement of critical structures 5

Tissue Diagnosis

• Preoperative core-needle biopsy is recommended for definitive diagnosis 1
• The biopsy track must be included in surgical resection if surgery is planned 1
• For skull base chordomas specifically, preoperative biopsy can be avoided in selected cases where imaging is characteristic and surgical planning is straightforward 1
• Immunohistochemistry for brachyury is strongly recommended to confirm the diagnosis, as brachyury is the diagnostic hallmark for conventional chordoma 1

Critical Pitfalls to Avoid

Do not mistake benign variants for pathology: In younger patients, consider benign entities like enlarged parietal foramina variants, which can present as multiple calvarial lytic lesions but have well-defined contours and no soft tissue component 6

Do not perform internal fixation if pathological fracture is present: This disseminates tumor and increases local recurrence risk; use external splintage instead 1

Do not delay tissue diagnosis in ambiguous cases: While imaging can be suggestive, definitive diagnosis requires histopathology, and treatment planning depends on accurate diagnosis 1

Management Implications

Treatment requires multidisciplinary approach in referral centers with expertise in skull base surgery, radiation oncology (particularly hadron therapy), and medical oncology 1

For skull base chordomas, R1-R2 surgery plus high-dose radiation therapy is the treatment of choice, as en bloc R0 resection is rarely feasible in this location without unacceptable morbidity 1

Hadron therapy (protons or carbon ions) should be considered the treatment of choice for radiation, with doses up to at least 74 GyE required due to relative radiation resistance 1