Extradural dermoid tumours of the posterior fossa

Abstract

Dermoid tumours in children usually occur in two locations: at the anterior fontanelle and on the occipital squama. An exceptional site of origin for a posterior fossa dermoid cyst is the extradural space. There are only six previous cases of this situation reported in the literature. A series of 103 subscalp and calvarial masses in children were reviewed and three children are reported with extradural dermoids of the posterior fossa, which communicated with the skin through midline occipital dermal sinuses. All three children were seen after the rapid growth or the formation of an abscess in a previously noted occipital subcutaneous mass present since birth. Although computed tomography or magnetic resonance imaging showed the dermal sinus and the intracranial tumour, these studies were unable to ascertain the intradural or extradural nature of the tumours, their exact origin only being established at operation.Histopathological study showed preclinical signs of infection in the two patients that had not yet formed an abscess. It is suggested that early neurosurgical treatment of these neoplasms should be done to prevent the development of severe intracranial infection. The previously reported simplicity of surgical removal of occipital extradural dermoids was not confirmed in this series.

Analysis of the growth pattern of a dermoid cyst

“…4,13,24 Reportedly, intracranial dermoid cysts do not cause symptoms until the lesion exceeds 3.0 cm in diameter. 14 In the occasional case reports describing dermoid cysts in the pediatric population, the cysts were associated with posterior fossa abscess formation and carried a high rate of mortality and morbidity. 26 This highlights the importance of early treatment of these lesions.…”

“…Gross-total resection whenever possible remains the mainstay of treatment for dermoid cysts. 6,14 However, this may not always be safely feasible; the cyst's capsule may be difficult to remove if it is tightly attached to surrounding parenchyma, nerves, or vasculature. 3,5,10,23 This can have particularly devastating sequelae if the capsule is adherent to the brainstem.…”

“…2,3,8,12,14,20,22 Unlike their slightly more common epidermoid counterparts, dermoid cysts tend to occur in the midline. They may be found anywhere throughout the neuraxis but only account for approximately 0.3% of all intracranial lesions.…”

“…3,7,11,17 Rarely, these lesions may also involve dural venous sinuses or brain parenchyma. 12,14 Up to one-third of all dermoid cysts are associated with dermal sinus tracts, which may predispose patients to recurrent episodes of septic meningitis. 12,14 Despite the fact that dermoid cysts are congenital abnormalities, they are usually discovered in young adults following an indolent course of symptoms related to mass effect, meningitis, hydrocephalus, or intracranial hypertension.…”

“…12,14 Up to one-third of all dermoid cysts are associated with dermal sinus tracts, which may predispose patients to recurrent episodes of septic meningitis. 12,14 Despite the fact that dermoid cysts are congenital abnormalities, they are usually discovered in young adults following an indolent course of symptoms related to mass effect, meningitis, hydrocephalus, or intracranial hypertension. Symptomatic occurrence in the pediatric population is uncommon, and the discovery of completely asymptomatic dermoid cysts in this age group is exceedingly rare.…”