Atypical meningioma - intraosseous
Cervical spine MRI performed for upper extremity weakness revealed cervical syrinx and Chiari malformation. Dedicated head imaging recommended for further evaluation.
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There is an expansile lesion centered in the right parietal bone, infiltrating and expanding the diploic space. The lesion is heterogeneously T1 and T2 hypointense and has areas of abnormally restricted diffusion.
The lesion measures 8 cm in maximal diameter and extends laterally into the adjacent soft tissues and medially into the epidural space. There is mild local mass effect with mild effacement of adjacent sulci, without associated increased T2/FLAIR hyperintensity in the brain parenchyma.
This may represent an intraosseous meningioma or fibrous dysplasia with other etiologies also possible. Head CT is recommended to further characterize the lesion.
Additional history elicited after MRI: 2 years of tender lump on the right side of the scalp.
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An expansile lytic and sclerotic bone lesion is centered in the right parietal bone. The lesion measures 8 cm in maximal diameter. The lesion extends anteriorly just beyond the coronal suture into the right frontal bone and inferiorly to the squamosal suture. The involved outer table is irregular and the inner table is spiculated. The lesion is associated with enhancing soft tissue that extends laterally about 3 mm into the adjacent scalp under the temporalis muscle and medially about 1 cm into the epidural space.
There is evidence of mild mass effect with mild effacement of the sulci in the adjacent right posterior frontal lobe. There is no underlying edema pattern or midline shift. Cortical veins overlie this region and may be partially encased by the soft tissue component.
Together with the long duration of symptoms, the appearance favors intraosseous meningioma, perhaps of a higher grade given the degree of bony erosion. Cavernous hemangioma is an alternative consideration but this lesion typically spares the inner table, which is involved on the current study. Fibrous dysplasia, which relatively rarely involves the calvaria, is unlikely because it typically preserves the inner and outer tables even when it causes osseous expansion. More malignant etiologies such as lymphoma and metastases, despite the restricted diffusion seen on MRI, are felt to be unlikely given the hyperostotic component and long duration of symptoms. Osteosarcoma is also unlikely given the long course.
The lesion was incidentally discovered but upon further history gathering, the lesion was symptomatic. Thus, the patient was planned for surgical resection. Preoperative lumbar puncture was performed given the imaging finding of empty sella; the open pressure was 10 cm of water, thereby excluding intracranial hypertension. The surgery consisted of right frontotemporoparietal craniectomy, cranioplasty, resection of intradural tumor, and duraplasty. Gross total resection was achieved.
Histopathology revealed that the lesion was an atypical meningioma, WHO grade II. Additional notes from the pathology report: The tumor shows areas of high cell density, focal necrosis, prominent nucleoli, and foci of patternless growth. The mitotic count is 3 per 10 high power fields. The Ki-67 proliferation index is 2.8%. The tumor diffusely involves bone, skeletal muscle, and dura.
On imaging, the fact that the lesion is centered in the bone is consistent with intraosseous meningioma, albeit this terminology is controversial when the lesion also extends outside the bone. Given the dural involvement, it may also be reasonable to call this an en plaque meningioma that subsequently extended into bone.
Given the histology, the patient underwent postoperative radiation to the resection cavity in an effort to minimize risk of neurologic morbidity from tumor recurrence.