Epidermoid and Dermoid

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Epidermoid and dermoid cysts are the most common tumors, accounting for up to 60% of the calvarial masses in the pediatric population.52,72 The lesions result when cutaneous ecto-dermal rests are included in the developing cranium. They grow within the diploe and expand and erode the outer and inner tables of the skull. Both epidermoid and dermoid cysts are lined by stratified squamous epithelium and contain keratin from desquamation. Because a dermoid also has skin appendages, its cyst may contain hair and sebum as well. Because the primitive ectoderm has the capacity to form all the epidermal and dermal elements, these cysts embryologically can all be der-moids. Some reports, especially in the older literature, do not differentiate between epidermoid and dermoid cysts. Also, the tissue sent for histopathologic examination may not reflect the lesion in its entirety, or the dermal elements may have been destroyed by inflammation.

Intradiploic epidermoids and dermoids are similar clinically and radiologically. They both typically occur as a painless mass. A plain radiograph shows a rounded osteolytic lesion with well-defined, sclerotic margins (Figure 102-1 A). The hypodense mass can be seen on CT scans eroding the inner

Golden Cystic Dermal Mass

FIGURE 102-1 Dermoid cyst. This 17-month-old girl presented with a left parietal, enlarging, nontender mass. A, The lateral skull x-ray film shows a round osteolytic lesion with a sclerotic margin. B, The computed tomography scan reveals more erosion of the outer table of the skull than the inner table, resulting in a beveled margin.

FIGURE 102-1 Dermoid cyst. This 17-month-old girl presented with a left parietal, enlarging, nontender mass. A, The lateral skull x-ray film shows a round osteolytic lesion with a sclerotic margin. B, The computed tomography scan reveals more erosion of the outer table of the skull than the inner table, resulting in a beveled margin.

skull table more than the outer table and sometimes expanding both (Figure 102-1B).4 Capsular calcification or enhancement occurs in rare instances.

The majority of dermoid cysts are located off the midline in the supraorbital region and along cranial sutures, but some cysts may arise in the midline, commonly at the anterior fontanel and occipital region (Figure 102-2).52,64 Dermoid cysts of the skull can also be seen in association with congenital dermal sinus (CDS).15 The CDS is a tract lined by stratified squamous epithelium. The tract is found in the midline in the region of the nasion or in the occipital area, with none entering the skull in the region occupied by the superior sagittal sinus.17,72 The tract may end just below the skin surface or extend intracranially through the foramen cecum to the crista galli from the nasion. The CDS can be associated with one or more inclusion cysts that vary in size from barely more than the diameter of the tract to a large tumor and can occur at any point along the tract; it has a preference, however, for the terminus. Because the abnormal connection between the dermal-ectoderm and neural-ectoderm that forms the CDS is small during early embryologic development, the disturbance in the mesoderm condensing around the tract is minimal. As a result, the distortion of the adjacent skull is insignificant, and detection of a bone defect with imaging studies can often be difficult. Also, the opening of the CDS on the skin surface may be so small as to escape detection, except with close inspection. Surrounding angiomatous changes may sometimes be present with these lesions, particularly in the occipital location. Hair may be seen to protrude from the orifice. Debris or purulent material may drain from the site. The depth to which the CDS penetrates and whether it is associated with one or more dermoid cysts will determine the clinical manifestation. A CDS often goes unnoticed until the patient has infection, most commonly subcutaneous; however, one can also see extradural or intradural abscesses and meningitis. Often, it is helpful to get both CT and MRI scans for evaluation of a CDS. The diagnosis of a CDS, however, is clinical, and imaging studies are only augmentative. A negative imaging study does not exclude the need to explore the tract to its end; however, such studies can be helpful in ascertaining if the CDS is associated with one or more dermoid cysts. Complete surgical excision of the mass with the capsule results in cure.

Skull Dermoid Cyst

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