Answer for BIR CoW 04 Aug 2024
Parasellar epidermoid cyst
Findings
Evidence of well defined T1 hypointense / T2 hyperintense extra axial lesion in right parasellar region, showing incomplete suppression on FLAIR with diffusion restriction and low ADC values. The lesion is seen involving right Meckel’s cave and right cavernous sinus displacing the cavernous segment of right internal carotid artery medially.The lesion is seen compressing right 5th cranial nerve.The lesion is measuring approximately 2.7 x 2.2 x 2.3 cm. The lesion is causing mass effect over right hemipons and posteromedial aspect of right temporal lobe.
Discussion
Meckel’s cave is a natural mouth-shaped aperture in the medial portion of the middle cranial fossa that acts as a key conduit for the largest cranial nerve, the trigeminal nerve.It connects the cavernous sinus to the prepontine cistern of the posterior fossa. Epidermoid tumors probably arise embryologically from incomplete cleavage of neural ectoderm from cutaneous ectoderm with inclusion epiblasts in the neural groove at the time of closure (3-5 weeks gestation).These tumors grow by desquamation of epithelial cells that break down into keratin and cholesterol within the tumor capsule. The soft pliable cholesterol and keratin produced by this process allow for slow growth. Epidermoid tumors are known to creep around or engulf intracranial structures. Cranial nerve deficits are thought to arise from resultant ischemia.In addition, leakage of tumor content is known to induce inflammation. Surprisingly, very few patients present with irritative symptoms, but more often report cranial nerve palsies or compressive symptoms.
IMAGING CHARACTERISTICS :
All epidermoids usually show low signal intensity on T1 - weighted images, high intensity on T2-weighted images, and lobulated margins conforming to the preexistent space with minimal mass effect.Although epidermoids contain cholesterol, they have low signal on T1 -weighted images and do not demonstrate increased signal as seen in some craniopharyngiomas. This difference in signal may be secondary to the varying physiologic state of cholesterol, which is solid in epidermoids and liquid in craniopharyngiomas.Epidermoids demonstrate restricted diffusion, incomplete FLAIR suppression and no gadolinium enhancement.Epidermoids in the cerebellopontine angle/prepontine cistern are much more proliferative, and extend into multiple cisterns with encasement of the basilar artery.
DIFFERENTIAL DIAGNOSIS :
Related to Trigeminal Nerve Common - Perineural spread of cancers Uncommon Nerve sheath tumours like schwannoma,CIDP, Infection - Herpes.Non-trigeminal causes Common-Meningioma,Leptomeningeal metastasis, Uncommon Vascular - Persistent trigeminal artery,Vascular loops,Lymphoma,Sarcoid,Pituitary macroadenoma,Petrous mucocele/cephalocele,Cholesterol granuloma/cholesteatoma,Chondroid lesions andICA aneurysms
REFERENCES :
MR Imaging of Primary Tumors of Trigeminal Nerve and Meckel’s Cave https://ajronline.org/doi/pdf/10.2214/ajr.151.3.577. Neuroimaging of Meckel’s cave in normal and disease conditions Received: 27 November 2017 / Revised: 24 January 2,Trigeminal Neuralgia Due to a Small Meckel’s Cave Epidermoid Tumor018 /Accepted: 1 February 2018 /Published online: 18 April 2018 # The Author(s) 2018
Findings
Evidence of well defined T1 hypointense / T2 hyperintense extra axial lesion in right parasellar region, showing incomplete suppression on FLAIR with diffusion restriction and low ADC values. The lesion is seen involving right Meckel’s cave and right cavernous sinus displacing the cavernous segment of right internal carotid artery medially.The lesion is seen compressing right 5th cranial nerve.The lesion is measuring approximately 2.7 x 2.2 x 2.3 cm. The lesion is causing mass effect over right hemipons and posteromedial aspect of right temporal lobe.
Discussion
Meckel’s cave is a natural mouth-shaped aperture in the medial portion of the middle cranial fossa that acts as a key conduit for the largest cranial nerve, the trigeminal nerve.It connects the cavernous sinus to the prepontine cistern of the posterior fossa. Epidermoid tumors probably arise embryologically from incomplete cleavage of neural ectoderm from cutaneous ectoderm with inclusion epiblasts in the neural groove at the time of closure (3-5 weeks gestation).These tumors grow by desquamation of epithelial cells that break down into keratin and cholesterol within the tumor capsule. The soft pliable cholesterol and keratin produced by this process allow for slow growth. Epidermoid tumors are known to creep around or engulf intracranial structures. Cranial nerve deficits are thought to arise from resultant ischemia.In addition, leakage of tumor content is known to induce inflammation. Surprisingly, very few patients present with irritative symptoms, but more often report cranial nerve palsies or compressive symptoms.
IMAGING CHARACTERISTICS :
All epidermoids usually show low signal intensity on T1 - weighted images, high intensity on T2-weighted images, and lobulated margins conforming to the preexistent space with minimal mass effect.Although epidermoids contain cholesterol, they have low signal on T1 -weighted images and do not demonstrate increased signal as seen in some craniopharyngiomas. This difference in signal may be secondary to the varying physiologic state of cholesterol, which is solid in epidermoids and liquid in craniopharyngiomas.Epidermoids demonstrate restricted diffusion, incomplete FLAIR suppression and no gadolinium enhancement.Epidermoids in the cerebellopontine angle/prepontine cistern are much more proliferative, and extend into multiple cisterns with encasement of the basilar artery.
DIFFERENTIAL DIAGNOSIS :
Related to Trigeminal Nerve Common - Perineural spread of cancers Uncommon Nerve sheath tumours like schwannoma,CIDP, Infection - Herpes.Non-trigeminal causes Common-Meningioma,Leptomeningeal metastasis, Uncommon Vascular - Persistent trigeminal artery,Vascular loops,Lymphoma,Sarcoid,Pituitary macroadenoma,Petrous mucocele/cephalocele,Cholesterol granuloma/cholesteatoma,Chondroid lesions andICA aneurysms
REFERENCES :
MR Imaging of Primary Tumors of Trigeminal Nerve and Meckel’s Cave https://ajronline.org/doi/pdf/10.2214/ajr.151.3.577. Neuroimaging of Meckel’s cave in normal and disease conditions Received: 27 November 2017 / Revised: 24 January 2,Trigeminal Neuralgia Due to a Small Meckel’s Cave Epidermoid Tumor018 /Accepted: 1 February 2018 /Published online: 18 April 2018 # The Author(s) 2018
Note:
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!