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INTRODUCTION
Meningiomas are the most common benign tumors among central nervous system (CNS) neoplasms1). However, meningiomas are rare in childhood and adolescence, representing only 0.4–4.6% of all CNS tumors5). Those located in intraparenchymaare much more rare without dural attachment3).
Intraparenchymal meningiomas, also considered as the same type of subcortical meningiomas, are defined as meningiomas located in brain parenchyma without dural attachment, occasionally reaching the brain surface2,4,6). To our best knowledge, there are only 18 intraparenchymal meningiomas in children re ported in the literature, with most of them in the cerebral lobes2,6–20).
Here we report the first case of primary intraparenchymal meningioma in the deep basal ganglia region in children and re view the pertinent literature to discuss the clinical presentation and management, radiological features, and possible pathogenesis. The significance in differential diagnosis of lesions in basal ganglia is also emphasized.
CASE REPORT
An 8-year-old boy presented at our hospital complaining of recurrent headache and vomiting for 3 months. The patient saw a doctor in a clinic before admission to our hospital and took some medicine for cold. The symptoms got relief temporarily but became severe 1 week ago.
Neurological examination showed impaired vision and mild paresis (IV-grade of muscle strength) of the left extremities. CT (Fig. 1A, B) revealed an iso- to hyperdense lesion in the right basal ganglion extending to superasellar cistern, 4.0×4.4 cm in size with peripheral calcification. No hyperostosis of sellaturcica was noticed (Fig. 1C). Magnetic resonance imaging (MRI) demonstrated most of the mass lesion was iso-intense on T1-weighted, T2-weighted and fluid-attenuated inversion recovery images with inhomogeneous enhancement (Fig. 2A–E). No duraltail sign was noted. Diffusion tensor image revealed the right pyramidal tract was partially disrupted.
Under the guide of navigation, a transcortical (through the right middle frontal gyrus) approach was adopted to explore the lesion. There was no dural attachment, but the tumor was tightly adhered with the anterior cerebral artery (ACA). Small vessels supplied the anterior aspect of the tumor, subtotal resection (STR) was achieved.
Histopathological examination revealed features of atypical meningioma with Ki-67 labeling index been approximately 10% (Fig. 3A–C). Immunohistochemistry showed the tumor positive for epithelial membrane antigen and negative for glial fibrillary acidic protein and S-100 protein (Fig. 3D–F).
The patient suffered transient exacerbation of impaired vision and weakness of contralateral limbs after operation, which resolved significantly after 3 months follow-up. Postoperative MRI revealed that most of the tumor had been resected and the residual part has been detached from dorsumsellae (Fig. 2F).
DISCUSSION
Clinical presentation
Primary intraparenchymal meningiomas are rare, but more frequent in children and adolescents than in adults7). To date, only 19 patients including ours, have been reported in the English-language literatures, which are summarized in Table 12,6–22). The age ranged from 0 to 18 years. Gender distribution showed a male dominance (n=14, 73.7%) in children and adolescents. The most common location was frontal lobe (n=8, 42.1%), followed by temporal lobe (n=5, 26.3%), parietal lobe (n=2, 10.5%), frontoparietal lobe (n=1, 5.3%), parietooccipital lobe (n=1, 5.3%), brainstem (n=1, 5.3%) and basal ganglia extending to superasellar cistern (our case, n=1, 5.3%). Presenting symptoms depend on tumor location and intracranial pressure, and seizure (n=13, 68.4%) was most frequent.
Management, features of histopathology and prognosis
Gross total resection (GTR) were achieved in 15 of 19 cases (78.9%). There was 70% remnant in one patient, because of the lesion in brainstem11). Another patient got subtotal resection, but the reason was not stated18). The study by Kotecha et al.14,16) showed that extent of initial surgical resection was the strongest independent prognostic factor for pediatric meningiomas and upfront radiotherapy achieved no benefit. Hence, GTR was the treatment of choice. In our case, STR was performed because of the rich blood supply, tight adhesion with ACA and lower tolerance of blood loss in children.
Zhang et al.34) and Starshak30) treated patients with malignant meningiomas with postoperative radiotherapy. However, postoperative radiotherapy was controversial. Some people thought meningioma could be induced by radiation23). Others suggested that adjuvant radiotherapy might delay recurrence of malignant meningiomas or progression of residual meningiomas24). Our case received postoperative radiotherapy because of the atypical meningioma and residual tumor growing.
Intraparenchymalmeningiomas were generally benign in children (n=11, 64.7%). Intraparenchymal atypical meningioma was first showed in zhang’s study2). In our patient, the lesion also proved to be atypical meningioma (World Health Organization-II).
The prognosis is worse in pediatric than in adult population, depending on the degree of excision, pathologic grade, tumor location and association with neurofibromatosis14,16,25). The 10-year recurrence rate for GTR and STR is 33% and 82%, respectively1). Hence, Kotecha et al.14,16) suggested the follow-up should be once every three months for at least 10 years and all life time for those with GTR or STR.
Differential diagnosis
The main radiological differential diagnosis for basal ganglia meningiomas includes gliomas, lymphomas and germinomas, but sometimes it is quite difficult by imaging findings alone. Generally, low grade gliomas are usually iso- to hypo-dense on un-enhanced CT scans, whereas germinomas and lymphomas are of high density5,12,21,24,28). With progression and emergence of apredominantly solid component, it is more difficult to distinguish non-typical meningiomas from gliomas, germinomas or lymphomas, all of which are iso-dense to hyper-dense on un-enhanced CT scans and relatively isointense on all MR pulse se quences5,12,21,24,28). Cystic changes, intratumoral hemorrhage and heterogeneous enhancement are more frequently seen in germinomas and gliomas24). However, with the similar large size, peritumoral edema and mass effect are usually slighter in meningiomas than in gliomas. Hence, clinical manifestation and other supplementary examinations should be considered in such cir cumstances. For instance, it’s helpful to identify germinomas with tumor markers in serum and CSF or lymphoma with elevated lymphocytes percentage in peripheral blood and CSF5,12,21,24,28). Careful evaluation of radiologic features should be emphasized, which would assist in selection of the preferred treatment for patients.
Pathogenesis of primary intraparenchymal meningiomas
The pathogenesis of primary intraparenchymal meningiomas is unclear. Some theories are proposed to explain the possible mechanism: 1) intraparenchymal meningiomas arise from arachnoid cells of the piamater, which enter the brain along with perforating blood vessels6,18,32,35); 2) the meningiomas, which arise from the piamater of brain sulcus, adheres and compresses the brain parenchyma, and grows into the intraparenchymal lesion, so the mass is seen to be completely buried in the parenchyma29); 3) some authors presume that the arachnoid cells rest during the migration progress6); 4) intraparenchymal meningiomas are believed to arise from ectopic meningothelial cells with in the stroma of the piamater6,18,32,35); and 5) the occurrence may be due to cellular dedifferentiation within the cerebral parenchyma, or they may arise from the sheath cells of cranial nerves, which is proposed as the similar mechanism for the equally uncommon cutaneous meningioma and intradiploic meningioma3). The first two theories are the most probable mechanisms to explain the origin in our case, based on the close relationship with the perforating arteries of ACA and middle cerebral artery and re current artery of Heubner, the imaging features and intraoperative findings.
CONCLUSION
For lesions of basal ganglion extending to the superasellar region, lack of dural attachment is the key neuroimaging feature for differentiating intraparenchymal meningiomas from tuber culum sellae, clinoid, sphenoid wing and cavernous sinus me ningiomas. Intraparenchymal meningiomas should be considered when gliomas, lymphomas, germinomas and other common lesions are excluded. The intraparenchymal atypical meningioma of basal ganglion in child is firstly reported, which should be emphasized in differential diagnosis to assist in selection of the preferred treatment for patient or avoiding a delay in management.
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