Presentations

Abstract

Introduction: Intracranial dermoid cyst refers to a typically benign mass which range from epidermoid cysts (made up of only desquamated squamous epithelium) to teratoma (made up essentially of any kind of tissue from all three embryonic tissue layers). Dermoid cysts account for approximately 0.5% of all primary intracranial tumors, typically present within the first three decades of life and are slightly more common in females. While often "benign" and discovered incidentally, these masses are not without symptoms or consequence. A long history of vague symptoms, with headache being the predominant feature commonly described. However, if large enough, complications from adjacent mass effect and seizures have been reported. Malignant transformation into squamous cell carcinoma, while extremely rare, has also been reported. Cyst rupture is another potential complication where fat like droplets can be seen layering along the cortical sulci, subarachnoid cisterns, and ventricles. Rupture may lead to chemical/aseptic meningitis and often present/responsible in symptomatic patients. Dermoid cysts have a characteristic appearance of a well-defined, low attenuating, lobulated mass on computed tomography (CT). Peripheral calcification may be seen within the walls. On magnetic resonance imaging (MRI), an intracranial dermoid will often show more variable signal characteristics being hyperintense on T1 sequences due to cholesterol/proteinaceous components as opposed while variable hypointense to hyperintense appearance on T2 sequences. Generally, these masses do not enhance on post contrast imaging, however in the setting of rupture, extensive pial enhancement may be present suggesting chemical meningitis.

Case Information: Patient presented to the emergency department as a trauma alert after motor vehicle accident (MVA). Patient reportedly had a seizure leading up to the accident, where patient subsequently crashed into a light pole at an estimated 35 miles per hour. Patient had altered mentation following the incident and was unable to provide information regarding their identity at initial presentation. Thus, patient was registered in the emergency department under an assigned pseudonym. Standard trauma protocol was followed, and patient underwent CT of the Head, Cervical spine, and Chest, Abdomen, and Pelvis. No traumatic sequela or abnormal findings were identified in the cervical spine, chest, abdomen, or pelvis. On the CT head, there was low attenuating substance seen throughout the subarachnoid space including along the cerebral sulci, subarachnoid cisterns and intraventricularly. Evidence of prior left temporoparietal craniotomy were identified. Additionally, there were more circumscribed and defined low attenuating collections were noted adjacent to the left temporal lobe, and along the high left frontoparietal cortex with peripheral calcification were noted. As the patient presented under an assigned pseudonym, access to prior imaging was initially unavailable. Clear evidence of traumatic sequela such intracranial hemorrhage or calvaria fracture were not identified. Patient was determined to be clinically stable and was subsequently discharged without further imaging or intervention.

Discussion/Clinical Findings: On initial assessment of a post-trauma CT head, evaluation for acute intracranial hemorrhage is paramount. Acute hemorrhage is classically hyper-attenuating in character. From initial "eyeball" test, intracranial low attenuation in the post traumatic setting may raise concern for pneumocephalus which can be seen following acute skull fracture. Fortunately, this can be confidently ruled out by utilizing the "region of interest" (ROI) tool which will report the average Hounsfield units (HU) of the region of interest. Hounsfield unit system is dimensionless and universally used in CT which provide a standardized numerical representation of attenuation. Gas will range in attenuation between from -500 to -1000 HU while fat/sebum ranges from -50 to -150 HU. Thus, with this distinction made and the lack of other identifiable post-traumatic sequela, ruptured dermoid with possible residual/recurrent dermoid was the leading diagnosis. None the less, the possibility of acute rupture and the possible complications such as chemical/aseptic meningitis being the etiology for patient's seizures must be considered. At the time of initial dictation, patient had recovered from their presumed post-ictal state and were able to provide information regarding their true identity. Thus, comparison to prior imaging could be performed. No-acute intracranial abnormalities were confirmed. Overall, there was a similar finding compatible with dermoid rupture and possible recurrent/residual dermoids.

Conclusion: Intracranial dermoid is a relatively uncommon intracranial mass which can be fairly confidently diagnosed given their characteristic appearance on CT and MRI. Despite their benignity, complications related to size and/or rupture ranges from headaches and seizure to vasospasm and even death. In conclusion, this case of ruptured dermoid is particularly intriguing given its relatively uncommon/rare nature, as well as its striking appearance on imaging and the potential diagnostic challenges this case may pose when evaluated as an unknown.