- Case report
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Infratentorial benign cystic meningioma mimicking a hemangioblastoma radiologically and a pilocytic astrocytoma intraoperatively: a case report
© Guan et al.; licensee BioMed Central Ltd. 2013
- Received: 16 April 2012
- Accepted: 10 October 2012
- Published: 28 March 2013
Cystic meningiomas are rare variants of meningiomas; they can pose a radiological diagnostic dilemma.
We present a rare case of a 30-year-old Chinese woman with a histopathological diagnosis of infratentorial cystic meningioma (World Health Organization Grade 1) in which the features in imaging modalities were suggestive of a hemangioblastoma. Intraoperatively, however, the gross macroscopic features were more in keeping with a pilocytic astrocytoma.
In benign cystic meningiomas, particularly the infratentorial variety, radiological findings utilizing the various imaging modalities and intraoperative impressions may not be reflective of or in keeping with the final histopathological diagnosis.
- Benign infratentorial cystic meningioma
- Pilocytic astrocytoma
Meningiomas are the most common primary non-glial intracranial tumors. They are commonly described as a solid tumor and account for between 10% and 20% of all intracranial tumors in adults. The incidence of meningiomas rises with advancing age and is more common in females. However, cystic meningiomas are uncommon and the incidence varies from 1.6% to 10.0% of all meningiomas. By contrast, cystic meningiomas are more common in males. Cystic meningiomas can pose a diagnostic dilemma radiologically. They can suggest other intracranial cystic masses: hemangioblastoma, astrocytoma, neuroblastoma or a metastatic tumor with a cystic or necrotic component. We present a case of an infratentorial cystic meningioma mimicking a hemangioblastoma radiologically and pilocytic astrocytoma intraoperatively.
A 30-year-old Chinese woman with a childhood history of acute lymphoblastic leukemia, currently in remission, presented to our Neurology clinic with a 3-week history of worsening headaches, giddiness and vomiting. The neurological examination revealed positive cerebellar signs in keeping with an infratentorial space-occupying lesion.
The tumor was approached via the infratentorial supracerebellar corridor with the patient in a prone position. Frameless neuronavigation using a fine-cut (1.2mm) contrast-enhanced CT brain scan was utilized in planning the surgical access. Gross total excision of the tumor was achieved under microscope assistance. The cystic component of the lesion contained xanthochromic fluid. The well-circumscribed solid component was a greyish, soft vascular lesion attached to the undersurface of the tentorium cerebelli. The wall of the cyst was smooth with no nodular lesion, suggestive of a pilocytic astrocytoma. The wall was not excised. The deep venous complex was visualized and preserved. A blood transfusion was not needed. The symptomatology improved post-operatively. She was discharged on the 4th post-operative day.
Centrally located intratumoral cysts
Peripherally located intratumoral cysts
Peritumoral cysts in the adjacent parenchyma and
Peritumoral cysts between the tumor and the adjacent parenchyma
Various pathophysiological mechanisms of cyst formation in meningiomas have been postulated. Peritumoral cyst and intratumoral cyst formation have different pathophysiological mechanisms. Peritumoral cysts may be caused by reactive gliosis, fibroblastic proliferation, the final stage of the intense peritumoral edema, a widening of the subarachnoid space, or mechanical trapping of the cerebrospinal fluid spaces. Conversely, intratumoral cysts are the result of microcystic degeneration, ischemic necrosis, or hemorrhage within the tumor. Malignant meningiomas have a higher incidence of cyst formation due to ischemic necrosis. Pathologically, intratumoral cysts are more common in the angiomatous and meningothelial variants as opposed to peritumoral cysts which are more common in the meningothelial variant.
In solid meningiomas the sensitivity of a CT brain scan is virtually 100% and the specificity is 90%, however, with cystic meningiomas, the diagnosis is made pre-operatively in less than 38% of cases. The presence of an enhancing nodule within a large cystic mass is a differential diagnosis along with other more common intracranial lesions like pilocytic astrocytoma and hemangioblastoma, especially in young adults, in which the appearances are similar. The commonest location of cystic meningiomas is in the cerebral convexity[2, 5] particularly in the frontal and parietal regions. The cerebral falx is the second most frequent location. In this case, the location of the lesion in the posterior cranial fossa and adjacent to the 4th ventricle, makes it difficult to determine radiologically whether the lesion is extra-axial or intra-axial.
Classically the MR imaging characteristics of a cystic meningioma have been described as an extra-axial lesion with enhancement of solid component and presence of a dural tail, which is thought to be due to increased vascularity and venous congestion within the adjacent meninges. In this case, the post-processed multiplanar MRI views showed that the lesion appeared to lie adjacent to the posterior falx, thus suggesting the possibility of an extradural origin. However, it did not exhibit any dural or cyst wall enhancement. Because a hemangioblastoma commonly presents as a well-circumscribed tumor with a solid mural nodule within a large cystic cavity, the difficulty of a radiological diagnosis arose. Furthermore, hemangioblastomas are typically found in the cerebellum in 83% to 86% of cases whereas cystic meningiomas are commonly found at the cerebral convexities, particularly at the frontoparietal regions. Odake describes three cases of cystic meningioma investigated by MRI and stated that “cystic meningiomas may not be differentiated from partly enhanced glioma or metastasis on MRI because of their non-enhanced cyst and focal oedema”.
An MRS of the enhancing solid component in this cystic meningioma did not help in differentiating between cystic meningioma and hemangioblastoma as both tumors showed an almost similar reduced N-acetylaspartate peak with increased choline-to-creatine ratio. It has been reported that the presence of high mobile lipid on proton MRS is more suggestive of hemangioblastoma, which was not seen in this case. However, the lipid peak on the MRS is non-specific and is also observed in other high-grade tumors such as high-grade gliomas, metastatic tumor, and anaplastic meningioma.
In benign cystic meningiomas pertaining to the infratentorial variety, radiological findings utilizing the various MRI sequences and MRS and intraoperative impressions may not be reflective or in keeping with the final histopathological diagnosis.
Written informed consent was obtained from our patient for the publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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