A 35-year-old man went to an outpatient clinic about a lump on the back of his head. It was growing, tender, and coming with worsening headaches. A skull X-ray showed a rounded lesion in the right parietal bone with a classic sunburst pattern, a finding that usually suggests a benign process.
The follow-up brain MRI is where the case turned. It picked up a second lesion he had no idea about: a dural-based mass on the midline of the posterior fossa, enhancing uniformly. That appearance strongly suggested a meningioma, the most common primary brain tumor.
It was not a meningioma. It took two separate rounds of pathology to establish that.
Two Chances to Get It Right, Two Wrong Answers
Surgeons resected the posterior fossa lesion, partly for diagnostic clarification and partly to head off future symptoms. During the operation, a frozen section went to pathology for a rapid read, the standard method for confirming what a surgeon is looking at while the patient is still on the table.
The frozen section came back compatible with a meningioma.
The permanent pathology, processed over the following days, said otherwise. It was a cavernous malformation, a benign cluster of abnormal, thin-walled blood vessels. Three months later, the calvarial mass on the back of his skull was excised too, and that turned out to be a second cavernous malformation. The case report was published in Radiology Case Reports.
The Scan That Would Have Flagged It, and Why It Was Skipped
Two details in the discussion make this case instructive.
The first is that the brain MRI was obtained out-of-network. The images were not available for direct review, only a detailed radiology report. The second is that cavernous malformations leak small amounts of blood over time, leaving deposits of hemosiderin, an iron-storage compound, in surrounding tissue, and certain MRI sequences are built to detect exactly that. Susceptibility-weighted imaging is more sensitive than the older gradient-echo technique and is the preferred sequence when a vascular malformation is suspected.
It was not obtained. The imaging had been optimized for surgical planning of a lesion everyone already believed was a meningioma.
The authors are careful about what that does and does not mean. The absence of signal on the gradient-echo sequences did have reduced suspicion for a hemorrhagic vascular lesion, but that finding does not exclude a vascular malformation. They also walked through why the alternatives looked unlikely: solitary fibrous tumor was doubtful given the uniform enhancement and lack of bony erosion, and dural metastasis was improbable in a 35-year-old with no surrounding swelling.
Every one of those judgments was reasonable. They were also, collectively, wrong.
A Two-Way Street of Radiologic Confusion
Cavernous malformations are not rare. They affect an estimated 0.4 to 0.6 percent of the population with no gender predisposition, and they usually sit within brain tissue rather than on the dura. When they turn up in a dural location, they start looking like tumors.
A case report in Cureus described a patient with chronic occipital headaches whose suspected meningioma proved at surgery to be a dural-based cavernoma. The authors noted that these lesions tend to be iso- to hypointense on T1, mixed to hyperintense on T2, contrast-enhancing, and hyperdense on CT, which are also typical meningioma characteristics. They add that dural cavernous angiomas can produce dural tails and hyperostotic reactions, features usually considered meningioma signatures, and that, in their own case, the lesion was even grossly encapsulated with the fibrous consistency of a meningioma. They were convinced until pathology said otherwise.
Others have reported the same pattern in different locations. One convexity dural cavernous malformation had eroded through the skull and initially presented as a soft scalp mass; the authors concluded that atypical dural-based lesions warrant further radiographic investigation before surgery.
The confusion runs both ways. A separate report documented an intraparenchymal meningioma mimicking a cavernous malformation, and a review of extra-axial cavernous angiomas catalogs how often these lesions are misread as something they are not.
Why Getting It Wrong Matters
The two conditions are managed with different logic.
Meningiomas are tumors. Depending on grade, location, and growth, they may be watched, resected, or treated with radiation, and higher-grade ones can recur and require ongoing surveillance.
Cavernous malformations are vascular. The concern is bleeding rather than tumor growth, and many are managed without surgery at all, particularly when they sit in deep or high-risk locations. Radiation therapy, a standard option for some meningiomas, is not the standard approach for cavernomas.
There is also an intraoperative dimension. A surgeon who opens the dura expecting firm, fibrous tumor tissue and encounters a cluster of thin-walled vessels is facing a different bleeding risk than anticipated.
None of this argues that imaging is unreliable in any general sense. MRI is extraordinarily good, and the vast majority of dural masses that appear to be meningiomas are indeed meningiomas. What this case illustrates is narrower: a confident imaging read can quietly narrow the protocol that would have caught the exception, and tissue remains the final word. Patients facing decisions about a brain lesion should discuss the diagnostic plan, including which imaging sequences are being obtained and why, with their neurosurgical team.
Key Questions Answered
What is a cavernous malformation?
A benign cluster of abnormal, thin-walled blood vessels. They affect an estimated 0.4 to 0.6 percent of the population and usually sit within brain tissue rather than on the dura.
How is that different from a meningioma?
A meningioma is a tumor arising from the membranes covering the brain. It is the most common primary brain tumor and is managed with observation, surgery, or radiation depending on grade and location.
What went wrong in this case?
Both the MRI and the rapid frozen section performed during surgery indicated a meningioma. Only the final permanent pathology identified a cavernous malformation.
Could imaging have caught it?
Possibly. Susceptibility-weighted MRI detects iron deposits from small bleeds and is preferred when a vascular malformation is suspected. It was not obtained because the scan was optimized for planning surgery on a presumed tumor.
Does the distinction change treatment?
Yes. Meningiomas may be resected or irradiated. Cavernous malformations are managed around bleeding risk, and many are observed rather than operated on.
Is imaging generally unreliable for brain lesions?
No. MRI is highly accurate, and most dural masses that resemble meningiomas are indeed meningiomas. This case documents an exception and the reason tissue diagnosis remains definitive.
