Prevalence: There are only three cases of epidermal scalp cysts reported prenatally3,5. Dermoid and epidermoid cysts account for 23 percent of all scalp lesions and there is a 2:1 female preponderance. The ethnic distribution is equal,.
Pathogenesis: Epidermal cysts are congenital tumors formed from pockets of ectoderm sequestered between the third and fifth week of embryonic life as the neural grove closes. This mechanism explains why most lesions are midline. They are typically found in the occipital region and over the anterior fontanelle1.
Sonographic findings: An epidermal scalp cysts presents as an extracranial cystic or heterogenous mass with no associated defect in the calvarium. Recognition of the absence of a defect in the calvarium is perhaps the most reliable aid in making the diagnosis. The mass is mobile and not attached to the underlying structures. The mass tends to remain cystic during the pregnancy, however, there is one reported case where the original cystic lesion regressed to a dense tissue mass.
Implications for targeted examinations: When an extracranial cystic mass is diagnosed parentally, a cephalocele is usually the primary consideration. If no defect is identified in the calvarium, the differential diagnosis would include a cystic hygroma, edema, teratoma, lipoma, or hemangioma. It is important to make an accurate diagnosis of the mass. An in-utero diagnosis of a cephalocele may lead to the termination of the pregnancy where as an epidermal scalp cyst is benign in nature. A careful search for a defect in the calvarium, normal intracranial contents, and associated anomalies is warranted.
Differential diagnosis: The differential diagnosis would include a cephalocele, meningocele, cystic hygroma, subcutaneous edema, cervical teratoma, lipoma, mesenchymal sarcoma, or hemangioma.
Associated anomalies: There are no reported associated malformations.
Prognosis: There are three cases of epidermal scalp cyst reported prenatally3,5. In two of the three cases, the cyst remained a small anechoic mass throughout the gestation as it did in our experience. One case reports the original cystic lesion had regressed to a dense tissue mass by 26 weeks gestation3. In all cases, no reported associated anomalies were identified. The prognosis is excellent. No intervention is required.
Recurrence risk: All cases are sporadic; therefore the recurrence risk is low1,2.
Management: Recognition of extracranial masses is important because of their benign nature. It is crucial to identify if a defect is present in the calvarium. When the bony defect is small the diagnosis is very difficult. A transvaginal scan with a high-frequency transducer or MRI may further delineate the mass and confirm that there is no intracranial extension. There have been at least two reported cases where the pregnancy was terminated for benign lesions. One was an occipital hemangioma and the other was an epidermal scalp cyst,. The presence of an extracranial mass must lead to a careful consideration of the differential diagnosis. When prenatal diagnosis of an epidermal scan cyst is made with confidence, no further intervention is warranted.
- Okaro E, Broussin B, Ville Y, Prenatal diagnosis of atypical cystic lesions of the fetal scalp. Ultrasound Obstet Gynecol 1998 Dec;12(6):442-4.
- Shahabi S, Busine A, Prenatal diagnosis of an epidermal scalp cyst simulating an encephalocele. Prenat Diagn 1998 Apr;18(4):373-7.
- Pryce DW, Khine M, Verbov JL, Van Velzen D, Scalp cyst with heterotopic brain tissue. Br J Dermatol 1993 Aug;129(2):183-5.
- Witkowski JA, Parish LC, Taping of a cyst: a method to facilitate removal of a scalp cyst. Int J Dermatol 1974 Jul-Aug;12(4):226.
- Nyberg DA, Mack LA. The spine and neural tube defects, In Nyberg DA, Mahoney SB, Pretorius DH, eds. Diagnositc Ultrasound of Fetal Abnormalities; Text and Atlax. Chicago: Year Book Medical, 1990:152-60.
- Pearce JM, Griffin D, Campbell S. The differential prenatal diagnosis of cystic hydromata and encephalocele by ultrasound examination. J Clin Ultrasound 1985;13:317-20.
- Winter TC 3
, Mack LA, Cyr DR. Prenatal sonographic diagnosis of scalp edema/cephalohematoma mimicking an encephalocele. Am J Roentgenol 1993;161:1247-8. Bronshtein M, Bar-Hava I, Blumenfeld A. Early sec0ond trimester sonographic appearance of occipital hamangioma simulating encephalocele. Prenat Diagn 1992, 12,695-698. Ferriman EL, McCormack J. An epidermal scalp cyst simulating an encephalocele. 1995 15,981-984. Takano Y, Yokokawa D, Namiki M, Toki D, Okuyama A. Perineal epidermal cyst. Urol Int 1994;53(1):53-5. Naidich TP, Altman NR, Braffman BH, McLone DG, Simmerman RA. Cephaloceles and related malformations, AFNR 1992;13,655-690. Martinez-Lage Sanchex JF, Almagro Navarro MJ, Poza Poza M. et al. Quiste dermoide de la fontanela anterior en el nino: significado clinico y distinction del encefalocele. 1992;An Esp Pediatr 36;355-358.