An Extremely Rare Case Report of Foramen Magnum Dermoid Cyst Presenting as an Acute Progressive Neurologic Deficit

Intracranial dermoid cysts are nonneoplastic lesions that present a rare clinical entity. They account for 0.04% to 0.6% of all intracranial tumors. Such cystic lesions usually contain different ectodermal derivatives including hairs, sebaceous glands, apocrine gland and teeth. Dermoid cysts of foramen magnum occur very rarely, with few cases reported in the literature. Computed tomography (CT) and magnetic resonance imaging (MRI) are two main diagnostic tools. Here in this paper, we described a case of intracranial (foramen magnum) dermoid cyst presented with neurologic deficits that completely removed surgically.


Introduction
Dermoid cysts are congenital ectodermal inclusion cysts that contain varying amounts of ectoderm derivatives. Epidermoid cyst generated from squamous epithelial cells and doesn't show dermal derivatives such as hair follicles. Teratomas consist of ectodermal, mesodermal and endodermal tissue [1] [2].
Clinical presentation of patients with brain dermoid lesions is variable. They may be incidentally detected on brain computed tomography (CT) or magnetic resonance imaging (MRI) for complaints such as head trauma or headaches.
They may cause a large mass effect and resulted in signs and symptoms related to compression of adjacent brain tissue structures [ [9]. Intracranial dermoid lesions are usually located in midline such as suprasellar region. They may also occur in parasellar region or posterior fossa and cerebellar vermis [10]. Here in this case report study we presented a middle-aged woman with neurologic deficits related to dermoid cyst in foramen magnum that was confirmed by MRI and also pathologic evaluations.

Case Presentation
The reported case is a 45-year-old woman presented with progressive gate problems and upper limb pain, paresthesia and weakness to the neurology clinic of    approach. The lesion has a distinct thin capsule which after opening liquid content with yellow color, fat like particle and a considerable amount of hair exited ( Figure 5).
Ten days after surgery patient was discharged and showed gradual alleviation in signs and symptoms in follow up. Now the patient is 10 months out from surgery without recurrent or residual tumor.

Discussion
Intracranial dermoid cysts are benign congenital dysembryogenic lesion that are usually located midline. They are caused by embryological malformation during the development of the neural tube between the 3rd and 5th weeks [11]. This squamous epithelium lined cysts contain skin appendages such as nails, hair follicles, teeth and sebaceous glands [12]. About seven percent of dermoid affect the head and neck. They are frequently presented at the orbit, nose or in the lateral eyebrow. The age of occurrence in woman is between 20 and 36 years of age [13]. Our case was 45 years old. Dermoid cysts can be seen in associated with Goldenhar (oculoauriculo-vertebral dysplasia) and Klippel-Feil syndromes, sporadically.
Cranial dermoid cysts comprise 0.04% to 0.7% of intracranial tumors and are four to nine times less common than epidermoid cysts. Most symptoms happen due to their mass effect on neural structures. The clinical presentations are depending on the location of intracranial lesions [14]. Most of such cases are frequently localized on the midline portion of the brain interesting sellar, suprasellar and frontonasal regions. Posterior cranial fossa is a less common localization. Our patient had a distinct mass in the foramen magnum.
The most prevalent symptoms include focal headache (32%), neurologic deficit, or meningitis. Less common presentations include visual field defects, seizures, exophthalmos, hydrocephalus, and oculomotor palsy [15]. Some cases of sudden death have also been reported followed by spontaneous rupture of dermoid cyst. In the present report, the patient was presented with progressive gate problems and upper limb pain, paresthesia and weakness.
An essential step in diagnosing these lesions is imaging studies. The differential diagnosis which is proposed based on the imaging findings includes epidermoid cysts, arachnoid cysts, cystic gliomas, lipomas, teratomas, and craniopharyngiomas [16]. On CT images, dermoid cysts appear as a uniloculated, well-delineated cystic mass with hypodensity from moderate to significant and some are present capsular calcification. MRI features include hyperintense signal on SE T1 sequences and heterogeneous hypo-hyperintense signal on FSE T2 [17].
Rupturing of dermoid cysts typically is seen as high-signal fat droplets within the subarachnoid spaces and intraventricular fat/CSF levels. In our case, the patient had no symptoms and signs of meningitis or hydrocephalus.
Surgical resection remains the treatment modality of choice. Tumors in foramen magnum can pose challenges for neurosurgeons [18]. By improving microsurgical techniques, the total resection is preferable. It is believed to reduce both postoperative chemical meningitis and tumor recurrence risk. Often the prognosis of patients with intracranial dermoid cysts who undergo surgery is favorable.

Conclusion
The presented case is such a rare radiologic finding that was successfully removed via surgery and precisely confirmed pathologically. We suggest that all clinicians especially radiologists, neurosurgeons and neurologists consider and keep dermoid tumor in their minds as the differential diagnosis of cystic lesions in foramen magnum. The preferred surgical planning can be guided by exact preoperative imaging.