Answer for BIR CoW 13 Feb 2022
EPIDERMOID CYST
Findings
Findings: An ill defined T1 hypo,T2 hyperintense lesion which is partially supressed on FLAIR seen probably arising from left cerebellopontine angle extending anteriorly into interpenduncular and left ambient cistern, posteriorly into left cerebellomedullary cistern, laterally into internal auditory canal and medially causing mass effect on pons. The lesion measures 4.1(anteroposterior )x2.1(transverse ) x 2.1(cranio caudal ) cms. Lesion shows areas of diffusion restriction and low ADC values with no gradient blooming. Post contrast images shows no evidence of contrast enhancement Impression Left cerebellopontine angle epidermoid cyst with extension into interpenduncular and left ambient cistern and abutting the left porus acousticus.
Discussion
Epidermoid cysts arise from the inclusion of ectodermal epithelial tissue during neural tube closure in the first weeks of embryogenesis. They contain desquamated stratified keratinized epithelium. They are the third most common mass lesion to occur within the CPA region behind vestibular schwannomas and meningiomas, accounting for approximately 5% of all CPA masses Epidermoid cysts have fluidlike signal characteristics on spin-echo T1- and T2-weighted sequences; therefore, they appear similar to CSF within the CPA cistern and similar to CSF-containing arachnoid cysts on these sequences. Typical epidermoid cysts do not enhance, and therefore administration of IV gadolinium does not reliably enable them to be visualized against the background of CSF on T1-weighted images. Although DWI can show clear elevation of signal within an epidermoid cyst and this may be crucial in the postoperative state to confirm the presence of residual tumor , DWI has relatively poor resolution compared with conventional anatomic MRI sequences and cannot depict the margins of the tumor relative to important cisternal structures such as intracranial vessels and cranial nerves Epidermoid cysts most often show mixed iso- to high signal intensity on FLAIR imaging that differentiates them from arachnoid cysts, which show complete signal suppression due to their CSF content [5]. However, CSF pulsation artifact within the adjacent posterior fossa cisterns may obscure the margins of epidermoid cysts. On MR cisternography, a heavily T2-weighted 3D sequence that depicts cisternal structures in fine detail, epidermoid cysts appear hypointense to CSF with lobulated margins. This allows their precise anatomic relationship to other cisternal structures such as vessels and nerves to be clearly depicted for surgical planning. Frank enhancement within an epidermoid cyst is extremely rare and may suggest malignant transformation into a squamous cell carcinoma
References
Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): 650-64. Radiology (full text) - doi:10.1148/radiol.2393050823 Chen CY, Wong JS, Hsieh SC et-al. Intracranial epidermoid cyst with hemorrhage: MR imaging findings. AJNR Am J Neuroradiol. 2006;27 (2): 427-9. AJNR Am J Neuroradiol (full text)- Pubmed citation
Findings
Findings: An ill defined T1 hypo,T2 hyperintense lesion which is partially supressed on FLAIR seen probably arising from left cerebellopontine angle extending anteriorly into interpenduncular and left ambient cistern, posteriorly into left cerebellomedullary cistern, laterally into internal auditory canal and medially causing mass effect on pons. The lesion measures 4.1(anteroposterior )x2.1(transverse ) x 2.1(cranio caudal ) cms. Lesion shows areas of diffusion restriction and low ADC values with no gradient blooming. Post contrast images shows no evidence of contrast enhancement Impression Left cerebellopontine angle epidermoid cyst with extension into interpenduncular and left ambient cistern and abutting the left porus acousticus.
Discussion
Epidermoid cysts arise from the inclusion of ectodermal epithelial tissue during neural tube closure in the first weeks of embryogenesis. They contain desquamated stratified keratinized epithelium. They are the third most common mass lesion to occur within the CPA region behind vestibular schwannomas and meningiomas, accounting for approximately 5% of all CPA masses Epidermoid cysts have fluidlike signal characteristics on spin-echo T1- and T2-weighted sequences; therefore, they appear similar to CSF within the CPA cistern and similar to CSF-containing arachnoid cysts on these sequences. Typical epidermoid cysts do not enhance, and therefore administration of IV gadolinium does not reliably enable them to be visualized against the background of CSF on T1-weighted images. Although DWI can show clear elevation of signal within an epidermoid cyst and this may be crucial in the postoperative state to confirm the presence of residual tumor , DWI has relatively poor resolution compared with conventional anatomic MRI sequences and cannot depict the margins of the tumor relative to important cisternal structures such as intracranial vessels and cranial nerves Epidermoid cysts most often show mixed iso- to high signal intensity on FLAIR imaging that differentiates them from arachnoid cysts, which show complete signal suppression due to their CSF content [5]. However, CSF pulsation artifact within the adjacent posterior fossa cisterns may obscure the margins of epidermoid cysts. On MR cisternography, a heavily T2-weighted 3D sequence that depicts cisternal structures in fine detail, epidermoid cysts appear hypointense to CSF with lobulated margins. This allows their precise anatomic relationship to other cisternal structures such as vessels and nerves to be clearly depicted for surgical planning. Frank enhancement within an epidermoid cyst is extremely rare and may suggest malignant transformation into a squamous cell carcinoma
References
Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): 650-64. Radiology (full text) - doi:10.1148/radiol.2393050823 Chen CY, Wong JS, Hsieh SC et-al. Intracranial epidermoid cyst with hemorrhage: MR imaging findings. AJNR Am J Neuroradiol. 2006;27 (2): 427-9. AJNR Am J Neuroradiol (full text)- Pubmed citation
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!