[Medulloblastoma presenting as an extra-axial tumor in the cerebellopontine angle]

Extra-axial desmoplastic/nodular medulloblastoma in adult mimicking cerebellar metastasis: reappraisal of this rare presentation with literature review

Introduction and importance

Medulloblastomas are the most common malignant intra-axial brain tumour in paediatric patients and represent 35-40% of posterior fossa tumour types in children between 3 and 9 years of age. Medulloblastomas may also be found in adulthood. These tumours are classified into two groups according to its molecular characteristics and histological type. The desmoplastic/nodular subtype is the second common subtype after the classic one. Only three cases of desmoplastic/nodular extra-axial medelloblastoma have been previously reported in the literature originating from to the cerebellopontine angle.

Case presentation

The authors report a new case of an extra-axial desmoplastic/nodular cerebellar medulloblastoma originating outside the cerebellopontine angle and mimicking a solitary cerebellar metastasis in a 49-year-old female patient who presented for a raised intracranial pressure and cerebellar syndrome.

Clinical discussion

Medulloblastoma is a malignant embryonal intra-axial tumour of the cerebellum or posterior brain stem that occurs mainly in children. Medulloblastomas may also be found in adulthood. Desmoplastic/nodular medulloblastoma is the second most common type of all medulloblastomas. The intra-axial form is always predominant. Only three cases of extra-axial desmoplastic/nodular medulloblastoma have been reported in the literature. The authors will go through the literature to dissect this rare entity.

Conclusion

Although considered a common paediatric intra-axial tumour, there are increasing numbers of solitary cases reporting an extra-axial presentation in different locations of the posterior cerebral fossa even in adulthood. These rare and unusual presentations and locations may mislead the correct diagnosis and delay treatment.

Extra-axial Desmoplastic Medulloblastoma in Adult Cerebellopontine Angle: Case Report and Noninvasive Molecular Subgrouping Utilizing Magnetic Resonance Imaging-Based Radiomics Nomogram

Cerebellopontine angle (CPA) is an atypical site for adult medulloblastoma (MB) with only 12 cases reported in pure extra-axial location. None was predicted on preoperative imaging while the most common misdiagnosis was petrous meningioma. We add the 13^th case to this list, attempting to reiterate the radiological features for preoperative prediction of this rare pathology on conventional magnetic resonance imaging (MRI). Molecular subtyping also is not yet reported for adult extra-axial CPA MB. We propose the routine use of MRI-based nomograms, in atypical CPA extra-axial masses, for noninvasive prediction of molecular subgroup, especially in resource-limited setups that lack the facility of genetic profiling.

Posterior fossa extra-axial variations of medulloblastoma: a pictorial review as a primer for radiologists

Manifestations of an atypical variant of medulloblastoma of the posterior fossa in extra-axial locations have been reported, and key questions concerning its interpretation have been raised previously. This review illustrated the clinico-radiological and histopathological features of the posterior fossa extra-axial medulloblastoma and described possible management strategies. We thoroughly reviewed all atypical anatomical locations of medulloblastoma reported within the posterior fossa and extra-axial spaces. The main characteristics of diagnostic imaging and histopathological results, primarily the distinctive radiopathological characteristics, were summarized to distinguish between intra- and extra-axial medulloblastoma, or pathologies mimicking this tumor. Most cases of posterior fossa extra-axial medulloblastoma have been reported in the cerebellopontine angle, followed by the tentorial and lateral cerebellar locations. The dural tail sign, which is commonly observed in meningioma, is rarely seen in intra- or extra-axial medulloblastoma and might be associated with other benign or malignant lesions. In addition to magnetic resonance imaging, the proposed new imaging techniques, including advances in modern neuroimaging modalities, were discussed, as potentially efficient modalities for characterizing extra-axial medulloblastoma. Radionuclide imaging and magnetic resonance perfusion imaging are practical alternatives to limit the number of differential diagnoses. We believe that medulloblastoma cases are likely under-reported because of publication bias and frequent tumors in unusual locations. Addressing these issues would help establish a more accurate understanding of this entity.

Review of cerebellopontine angle medulloblastoma

Cerebellopontine angle (CPA) medulloblastomas (MB) are rare lesions with few cases previously described in the literature. We report two further cases of CPA MB. The patients were a 22-year-old man and a 26-year-old woman with a mass developing in the CPA. The preoperative radiological diagnosis was vestibular schwannoma in the first case and petrosal meningioma in the second case. The patients were operated on through a retrosigmoid approach. The intraoperative findings revealed an intra-axial tumour and the histological diagnosis was classic type of MB in both cases. We review the literature and discuss pathological and radiological features and possible pathogenesis of CPA MB, underlining the necessity to consider MB in the differential diagnosis of CPA lesions.

Adult medulloblastoma and the "dural-tail" sign: rare mimic of a posterior petrous meningioma

The authors describe clinical and radiological features of a 32-year-old male patient with a posterior fossa lesion. The radiological characteristics resembled an extra-axial lesion; a meningioma, with attachment to the tentorium and petrous bone. The histological diagnosis was classical medulloblastoma. We review literature of this atypical presentation of medulloblastoma and "dural-tail" sign, which can be associated with other benign or malignant lesions. The role of magnetic resonance spectroscopy in the diagnosis of primitive neuroectodermal tumors is discussed.

Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions, skull base lesions that may invade the CPA region, and non-enhancing extra-axial lesions

Computed tomography (CT) and magnetic resonance (MR) imaging reliably demonstrate typical features of vestibular schwannomas or meningiomas in the vast majority of mass lesions responsible for cerebellopontine angle (CPA) syndrome. However, a large variety of unusual lesions can also be encountered in the CPA. Covering the entire spectrum of lesions potentially found in the CPA, these articles explain the pertinent neuroimaging features that radiologists need to know to make clinically relevant diagnoses in these cases, including data from diffusion- and perfusion-weighted imaging or MR spectroscopy, when available. A diagnostic algorithm based on the lesion's site of origin, shape and margins, density, signal intensity and contrast material uptake is also proposed. Non-enhancing extra-axial CPA masses are cystic (epidermoid cyst, arachnoid cyst, neurenteric cyst) or contain fat (dermoid cyst, lipoma). Tumours can also extend into the CPA by extension from the skull base (paraganglioma, chondromatous tumours, chordoma, cholesterol granuloma, endolymphatic sac tumour). Finally, brain stem or ventricular tumours can present with a significant exophytic component in the CPA that may be difficult to differentiate from an extra-axial lesion (lymphoma, hemangioblastoma, choroid plexus papilloma, ependymoma, glioma, medulloblastoma, dysembryoplastic neuroepithelial tumour).