Metronidazole induced toxicity
Bilateral symmetric high T2 & FLAIR signal involving the dentate nuclei of the cerebellum. The appearance favors metabolic conditions particularly toxic leukoencephalopathy.
* Presenting with dizziness, vertigo and loss of coordination
What is it?
A focal expansile single lesion.
How is it like?
* With moderate perilesional edema and mass effect deforming the 4th ventricle without signs of active hydrocephalus (not shown)
* With avid enhancement
Where is it?
Left posterior fossa.
Is the lesion intraaxial (cerebral hemisphere) or extraaxial (cerebellopontine angle)?
Suggestive of extraaxial location:
1) Peripheral location and wide dural contact
2) Changes in the adjacent skull vault bone
3) Dural Tail
Definitive for extraaxial location:
1) CSF cleft.
2) Interposed vessels, cortex or dura.
The lesion is intraaxial, located in the left cerebellar hemisphere.
Which are the differentials for intra- and extraaxial posterior fossa tumours?
DIFFERENTIAL DIAGNOSTIC FOR INTRAAXIAL POSTERIOR FOSSA TUMOUR
* HEMANGIOBLASTOMA: Most frequent posterior fossa primary tumour in adults. Strong association with von Hippel Lindau disease. Cystic tumour with mural peripheral solid avidly enhancing nodule. Perilesional pathologic vessels.
* METASTASES: Most frequent posterior fossa tumour in adults. Expanisve focal lesion, single or multiple, well defined, solid-necrotic, great edema, and mass effect.
* GLIOMA: Pilocytic astrocitomas (cystic tumour with solid mural nodule) and diffuse brainstem gliomas (often low-grade, infiltrative, ill-defined lesions without enhancement) much more common in peadiatric population. High-grade gliomas (infiltrative ill-defined lesions with heterogeneous enhancement and necrosis) are uncommon in the posterior fossa.
* MEDULLOBLASTOMA: Paediatric population (more common): Intraventricular, midline; young adults; parenchymal, paramedial, focal solid enhancing lesion. Different subtypes that share hypercellularity as main feature: CT hyperdense, T2 Hypointense and difussion restriction. High propensity for CSF dissemination.
* LYMPHOMA: Focal solid enhancing single lesion or multiple cloud-like enhancing lesions. Hypercellularity as main feature: CT hyperdense, T2 hypointense and diffusion restriction.
* SUBEPENDYMOMA: Adults, intraventricular 4th ventricle. Plastic. None or little enhancement.
The bulk of the tumour is within the ethmoid sinuses extending inferiorly into the nasal cavity and superiorly into the intracranial cavity through the cribriform plates
What is the lesion like?
Enhancing soft-tissue tumor expanding the ethmoid sinuses and nasal cavity
What are the MRI signal characteristics?
Mixed signal intensity on T2, low signal on T1, and intense enhancement on post-contrast images
What is the differential diagnosis of paranasal sinus tumour?
* Olfactory neuroblastoma: involves the ethmoid sinuses and extends through the cribriform plate into the anterior cranial fossa. Usually, shows intense enhancement and may show calcifications. They are slow growing with sinus expansion
* Juvenile angiofibroma: benign locally aggressive vascular tumor that affects adolescents. It is usually lobulated and expands the sphenopalatine foramen. Intense enhancement on post-contrast images
* Sinonasal carcinoma: heterogeneously enhancing mass that erodes the bone and may extend into the orbits or intracranially
* Lymphoma: low T2 signal with intense contrast enhancement and usually expands the bone
* Extra-axial CP angle mass.
* Heterogenous low signal intensity on T2.
* Intense enhancement on post-contrast images with thickening and enhancement of the tentorium cerebelli.
* No intracanalicular extension. Differential diagnosis: Schwannoma, ependymoma, metastasis