In our study, we conducted a comprehensive literature search in the PubMed database using the following search strategy: "(((parietal) OR ((supratentorial) OR (supra tentorial)))) AND (((medulloblastoma) OR (PNET)) OR (primitive neuroectodermal tumor) AND (adult))". Our most recent search update, performed on September 7, 2023, yielded a total of 279 articles. After excluding review articles and pediatric cases mentioned solely in the title and abstract, we meticulously examined the full text of the remaining articles. Based on the available pathological and imaging data in the literature, our case represents a unique instance—the first reported occurrence of parietal lobe metastasis in an adult with desmoplastic/nodular medulloblastoma.
Medulloblastomas are rare among adults, with an annual incidence varying between 0.5 and 20 cases per 1 million individuals.(8) These neoplasms are categorized as high-grade embryonal tumors based on their histological features and cellular origin. Historically, medulloblastomas were grouped with other embryonal tumors under the primitive neuroectodermal tumors (PNET) classification. However, they are now acknowledged as a separate entity. However, according to the WHO classification, they are now recognized as a distinct entity, encompassing classic medulloblastoma, desmoplastic/nodular medulloblastoma, medulloblastoma with extensive nodularity, and large-cell/anaplastic medulloblastoma. Additionally, Medulloblastomas are further
divided into four subcategories: wingless (WNT) activated, sonic hedgehog (SHH) activated, group 3, and group 4, according to the molecular pathways responsible for their development.(9)
In addition to physical examinations, the diagnosis of medulloblastomas relies on Brain CT and MRI scans. On CT imaging, medulloblastomas appear hyperdense, while MRI shows iso-intensity or hypointensity in T1-weighted imaging and hyperintensity in T2/FLAIR (fluid-attenuated inversion recovery) imaging.(10)
They commonly present with hydrocephalus and cerebellar dysfunction symptoms, such as nausea/vomiting, headache, unsteady gait, and truncal ataxia. Metastases typically occur in the posterior fossa, spine, and bones.(11) Supratentorial metastasis of adult medulloblastoma is scarce, primarily involving the frontal lobe, sub-frontal region, or cribriform plate. Kumar et al. reported two cases, aged 31 and 20 years, with supratentorial metastases occurring 3½ years and 11 months after the complete removal of posterior fossa medulloblastoma. Both patients underwent craniospinal irradiation; notably, the first case also developed spinal metastasis.(12)
Surgery is the primary treatment for all MB patients, aiming to achieve the most radical excision possible. The surgical goals include relieving the mass effect, restoring CSF circulation, obtaining diagnostic tissue, and reducing tumor burden. While complete resection is considered the standard approach upon diagnosis, the extent of survival advantage between this and near-total resection (removal of over 90% of the tumor) remains uncertain. As surgery alone carries a high recurrence risk, adjuvant radiotherapy is crucial in MB treatment.(13,14)
Radiation therapy usually commences approximately 3 to 4 weeks after surgery. The treatment involves irradiating the entire craniospinal axis, called craniospinal irradiation (CSI).(14) Adult medulloblastoma patients classified as high-risk, which includes individuals with large cell or anaplastic medulloblastoma, supratentorial primitive neuroectodermal tumors (PNETs), disseminated disease, tumors that cannot be surgically removed, or residual tumors exceeding 1.5 cm after surgical intervention, are subjected to the standard dose of craniospinal irradiation (CSI) and radiation targeted at the posterior fossa. Additionally, chemotherapy is an integral component of the therapeutic regimen in pediatric cases. Standard adjuvant chemotherapeutic regimens include cisplatin, carboplatin, and etoposide with or without cyclophosphamide.(15) However, routine chemotherapy in adult patients remains controversial.
In cases where hydrocephalus is present, the consideration of ventricular shunting may be required either prior to or following surgery. Nevertheless, certain patients may be able to avoid the need for shunting by effectively managing hydrocephalus through primary decompression and the restoration of cerebrospinal fluid (CSF) pathways.(16)