Skull base solitary fibrous tumor recurs despite mitotic count in WHO grade 1 rangeSurgery for skull base tumor shows risk of local recurrence
Frontiers in MedicinePublished October 21, 2026DOI ↗Editorial oversight: Dr. Lars van Dijk, PhD · Surgical, Procedural & Diagnostic
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Key Takeaway
Interpret mitotic count within the full clinical and proliferative context in skull-base SFT.
This is a single case report describing a 60-year-old woman with a right temporal skull base solitary fibrous tumor who underwent right frontotemporal microsurgical resection. Gross-total macroscopic removal was achieved, but the resection was piecemeal, so microscopic margins could not be assessed.
Histopathology showed 4 mitoses per 10 high-power fields, focal necrosis, nuclear STAT6 expression, weak partial CD34 expression, MDM2 immunoreactivity, and a Ki-67 labeling index of approximately 40%. The mitotic count falls within the CNS WHO grade 1 range.
Despite gross-total removal, tumor recurrence was documented at 18 months, with further enlargement at 27 months. No adverse events or tolerability data were reported.
The authors note that piecemeal resection limited margin assessment. They argue that a mitotic count in the grade 1 range does not exclude clinically significant local recurrence in skull-base solitary fibrous tumor, and that formal grading should be interpreted alongside anatomic extent, margin assessability, proliferative features, and certainty of local control.
This report illustrates a single clinical scenario and does not provide evidence for general clinical guidelines. It should not be used to change practice without corroboration from larger studies.
How this fits prior evidence
This case extends prior coverage of proliferative features in recurrent solitary fibrous tumor. A prior report noted a Ki-67 index rising from 15% to 70% in a recurrent intracranial tumor, reinforcing Ki-67 as a marker of proliferative activity. Here, a Ki-67 of approximately 40% accompanied recurrence at 18 months despite a mitotic count of 4 mitoses/10 high-power fields, within the CNS WHO grade 1 range. Separately, prior coverage described robot-assisted laparoscopic R0 resection for a giant pelvic solitary fibrous tumor. Together, these reports highlight that local control and proliferative biology vary by anatomic site and margin assessability, but none provide generalizable evidence.
When a tumor grows near the skull base, doctors must balance the goal of removing the mass with the difficulty of reaching every edge. A 60-year-old woman underwent surgery to remove a solitary fibrous tumor located at the base of her skull. While the surgeons were able to remove the entire visible mass during the procedure, the case highlights a tricky reality of these specific tumors.
Tests showed the tumor had some features of a low-grade growth, but it still grew back. The tumor reappeared at 18 months and grew larger by the 27-month mark. This happens because the area is hard to reach, making it difficult for doctors to ensure every microscopic cell is gone.
This case serves as a reminder for doctors and patients. Even if a tumor looks less aggressive under a microscope, its location and the difficulty of the surgery can still lead to it coming back. It shows that the physical location of a tumor is just as important as its biological grade when planning treatment.
What this means for you:
A low-grade skull base tumor can still recur even after a successful surgical removal of the main mass.
Common questions
Can a low-grade tumor still come back after surgery?
Yes. In this case, the tumor had a mitotic count within the range of a grade 1 tumor. However, it still showed signs of growth and recurrence at 18 months and 27 months. This shows that a low grade on a lab test does not always mean the tumor will stay away.
What is a solitary fibrous tumor?
A solitary fibrous tumor is a type of growth that can occur in various parts of the body. In this specific case, it was located at the skull base. These tumors can be difficult to treat fully because of their location near the brain and skull.
Why did the tumor come back in this patient?
The tumor was located at the skull base, where it is hard to reach. Because the surgery was done in pieces, it was impossible to check if the edges were completely clear. This makes it hard to tell if any tiny pieces were left behind.
BackgroundSolitary fibrous tumor (SFT) is a rare fibroblastic mesenchymal neoplasm of the central nervous system, and temporal skull-base lesions with destructive osseous change and extension toward the middle-ear region are uncommon.Case presentationA 60-year-old woman presented with acute right peripheral facial weakness. CT demonstrated expansile mixed lytic-sclerotic destruction of the right temporal bone and middle cranial fossa floor, and MRI showed a 46 × 38 × 36 mm lobulated mass with heterogeneous signal, irregular peripheral and nodular enhancement, central nonenhancing necrotic or cystic change, and adjacent temporal-lobe edema. Right frontotemporal microsurgical resection achieved gross-total macroscopic removal, although piecemeal resection rendered microscopic margins unassessable. Histology and immunohistochemistry supported SFT, with 4 mitoses/10 high-power fields, focal necrosis, nuclear STAT6 expression, weak partial CD34 expression, MDM2 immunoreactivity, and a Ki-67 labeling index of approximately 40%. Review of the available sections showed no morphologically distinct high-grade sarcomatous component. Under the 2021 CNS WHO framework, the documented mitotic count corresponds most closely to grade 1. Postoperative radiotherapy was recommended but declined. Telephone follow-up indicated that outside-hospital MRI reportedly showed tumor recurrence at 18 months and further enlargement at 27 months. The patient also reported that outside examinations showed no metastatic disease in the lungs, liver, or skeleton. During later follow-up, the family expressed concern that the patient might not tolerate another major surgical intervention, and continued clinical and imaging follow-up was recommended.ConclusionThis case illustrates that a documented mitotic count within the CNS WHO grade 1 range does not exclude clinically significant local recurrence. In skull-base SFT, formal pathologic grading should be interpreted together with anatomic extent, margin assessability, proliferative features, and the certainty of local control when planning postoperative management and surveillance.
