Keywords
dermoid cysts - child - frontal bone - neuronavigation
Introduction
Dermoid cysts are uncommon soft tissue lesions composed of squamous, epithelium-lined
sacs.[1] The cyst develops during gestation and is generally characterized by a midline location.
The wall of the cyst contains sweat glands and sebaceous glands that secrete fluid
into the cyst cavity. This causes a hyperintense signal in T1-weighted imaging.[2]
[3] Clinically, it presents as a raised lump or mass. We report an atypical case of
a patient with an intraosseous dermoid cyst, presenting as a lesion noticed as a raised
lump and located off the midline.
Case Report
A 2-month-old female presented with a fluid collection within the deep scalp appearing
to overlie a calvarial defect with possible intracranial extension visualized on ultrasound.
At approximately 7 months of age, the patient underwent a head computed tomography
(CT), which revealed a chronic appearing, small calvarial defect in the inferior right
frontal region immediately anterior to the coronal suture ([Figs. 1] and [2]). It measured approximately 6 mm in greatest dimensions. There were beveled sclerotic
margins, and an associated defect appeared to extend through the inner table of the
right frontal bone. At 18 months, a repeat head CT revealed the lesion had expanded,
demonstrating increased bony remodeling ([Figs. 3] and [4]). The diameter of the lesion grew to approximately 14 to 15 mm. It was decided to
excise the lesion due to progression in size. The patient underwent resection of the
lesion by supratentorial craniectomy with use of neuronavigation, followed by cranioplasty.
The mass was removed in a piecemeal fashion until the entire visible portion was removed.
The presence of cottage cheese-like material emanated from the diploic spaces of bone,
a finding generally consistent with a dermoid cyst, which was confirmed on histopathologic
examination. The craniotomy defect measured approximately 12 × 17.5 × 20 mm after
the mass was removed. Cranioplasty was then performed by applying autologous bone
chips to the surface of the dura and overlaying them with a moldable demineralized
bone putty.
Fig. 1 Initial head CT with bony reconstruction demonstrating lytic lesion. CT, computed
tomography.
Fig. 2 Initial head CT bony window with overlying radio-opaque marker demonstrating expansile
lesion. CT, computed tomography.
Fig. 3 Follow-up CT demonstrating expansion of bony lesion on bony reconstruction. CT, computed
tomography.
Fig. 4 Follow-up CT demonstrating expansion of diploic space with relative preservation
of inner and outer cortices. CT, computed tomography.
Discussion
Dermoid cysts are uncommon, slow-growing congenital lesions. Their differential diagnosis
includes dermoid cyst, cavernous hemangioma, eosinophilic granuloma, Langerhans cell
histiocytosis, and fibrous dysplasia.[4] Pediatric patients are the main population affected by dermoid cysts, as most develop
during gestation and become symptomatic early in life. This occurs in response to
entrapment of the ectoderm surface along the lines of embryonic fusion. The lesion
commonly appears superficially along the cranial sutures or anterior fontanelle.[1]
[5] They are benign but produce keratin and sebaceous material that is deposited into
the cyst cavity.[2]
[5] This results in the formation of an oily mixture inside the cyst. As secretion continues,
increasing intracystic pressure can result in mass effect or rupture.[2] Consequently, this heightens the risk of cranial erosion and expansion in the epidural
space.[5]
Dermoid cysts can occur in many locations of the body, but cysts of the head and neck
are commonly located at the frontotemporal or brow region.[3] They often present as a benign, painless lump under the scalp. Occasionally, they
are noticed as a palpable bony defect, as in this case.[6] Pryor et al performed a retrospective review of pediatric patients presenting with
dermoid cysts of the head and neck and found that 61% of the cysts were located in
the periorbital region. Due to its close proximity to the orbital region, cysts found
in this area can cause symptoms of headache, proptosis, visual disturbances, and development
of extradural hematomas. Only 10% of patients presented with cysts located in the
skull.[7] This cyst presented in the right frontotemporal region of the patient's calvarium
and was unusual because it was not in the midline. Additionally, it was intradiploic,
a rare subtype of frontotemporal dermoid cysts accounting for only 0.4 to 0.7% of
all cranial masses.[8] An indication that the cyst arose from the diploe is if the local dura remains unaffected
in addition to eroding inner and outer tables of the skull.[9]
[10]
