Differential Diagnosis for a 5 mm Focus of T1 Shortening at the Foramen of Monro
- Single most likely diagnosis
- Colloid cyst: This is the most likely diagnosis given the specific location at the foramen of Monro and the characteristic T1 shortening on MRI, which is typical for colloid cysts due to their high protein content.
- Other Likely diagnoses
- Neurocysticercosis: Although less common in this specific location, neurocysticercosis can present with cystic lesions that may show T1 shortening due to the scolex or inflammatory response.
- Rathke's cleft cyst: These cysts can occur in the suprasellar region but can occasionally be found near the foramen of Monro. They may show T1 shortening due to the presence of mucoid or proteinaceous material.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Glioblastoma or other high-grade gliomas: Although rare to present as a small, focal lesion with T1 shortening, aggressive brain tumors can have variable appearances and must be considered to avoid delayed diagnosis.
- Metastasis: Brain metastases can have a wide range of appearances on MRI, including T1 shortening, especially if they are hemorrhagic or have high protein content.
- Central nervous system lymphoma: This can present with a variety of imaging findings, including lesions that might show T1 shortening, particularly if there is hemorrhage or high cellularity.
- Rare diagnoses
- Choroid plexus cyst: While typically found within the choroid plexus of the ventricles, a choroid plexus cyst could potentially be located near the foramen of Monro and show T1 shortening.
- Epidermoid cyst: These cysts are rare and usually present with characteristic CSF-like signal on all sequences, but in some cases, they might show T1 shortening due to the presence of keratinaceous material.
- Dermoid cyst: Similar to epidermoid cysts, dermoid cysts are rare and can contain material that shortens T1, such as fat or sebaceous material, although their location at the foramen of Monro would be unusual.