When a glabellar dermoid cyst is not the whole story: the significance of MRI in excluding intracranial segments

Background Epidermoid and dermoid cysts are one of the most common benign pediatric tumors of the skull. Ultrasonography is usually the diagnostic tool of choice for their evaluation and diagnosis. Although benign, local growth with cosmetic issues, bone erosion, and occasional intracranial involvement generally warrant surgical resection. Since epidermoid and dermoid cysts may be seen by a wide range of medical disciplines, standardized recommendations for optimal diagnosis and treatment are necessary. Case presentation We report the case of a 14-month-old boy, who underwent neurosurgical removal of a glabellar dermoid cyst classified as an extracranial lesion, and in whom an intracranial lesion was identified on follow-up MRI, represents a rare and unusual clinical course. Ten months after surgery, a surveillance MRI revealed an intracranial lesion in the right frontal parasagittal region, while the child had developed no symptoms. Very careful retrospective review of the initial MRI suggested that an extremely small intracranial part of the lesion might have been faintly visible upon knowledge of the further clinical course. The intracranial lesion was subsequently resected and diagnosed as an epidermoid cyst. In our mini-review, we have compiled evidence that intracranial extension is more common than expected and particularly occurs in craniofacial midline lesions but is definitely not restricted to them. Conclusion Together, this case and literature review highlight the importance of careful preoperative assessment and interdisciplinary discussion to adequately determine the extent of craniofacial dermoid and epidermoid cysts before surgery. This case illustrates that a subtle intracranial lesion may not be recognizable on initial image interpretation despite MRI having been performed. Imaging follow-up is definitely recommended when intraoperative findings raise concern about deeper extension.