SAMIR S.SHAHMD, MSCE
Magnetic resonance imaging revealed a 1.5-cm cystic scalp lesion in the midline just superior to the cerebellum. Its enhancement paralleled the cerebrospinal fluid enhancement on all sequences, and it overlaid a skull defect. Craniectomy and excision revealed a meningocele.
Most scalp lesions are benign; however, up to 37% of solitary, nontraumatic scalp nodules extend intracranially to the dura mater or brain.1A midline location suggests embryologic abnormalities with potential for intracranial communication. At 3 to 5 weeks of development, the cranial neural tube fuses at the midline, followed by separation of the surface ectoderm away from the neural tube.2Defective midline fusion results in dysraphism. The differential diagnosis for a congenital midline scalp nodule includes cephaloceles, dermoid cysts, and heterotopic brain tissue in addition to more common entities such as hemangiomas and lipomas. Similarly, a midline scalp ulceration raises concern for aplasia cutis congenita (ACC) and underlying embryologic malformation.
The term cephaloceledescribes herniation of intracranial structures through a scalp defect and includes meningocele, encephalocele, and meningoencephalocele. These defects appear as pink or blue compressible nodules that pulsate or fluctuate with activity. They are frequently located on the parietal or occipital midline of the scalp.3Cephaloceles vary in size, with some lesions presenting as small plaques and others affecting a significant portion of the scalp. The hair collar sign, a band of thick, dark, coarse hair encircling the scalp nodule, is common with cephaloceles.2- 4It is also seen with heterotopic rests and ACC. While not specific, its presence mandates radiologic workup for intracranial communication.4,5
Dermoid cysts are common childhood scalp nodules and are also a consequence of abnormal fusion.1They are composed of disorganized dermal and epidermal tissue, are typically 1 to 4 cm, and are noncompressible. Often they are located along fusion lines, including the glabellar region, the posterior scalp, and the lateral brow, although the latter rarely shows intracranial extension.1Midline location or an overlying dimple or sinus ostia are particularly concerning for an intracranial communication. Intracranial communication is present in 11% of midline cysts, is found almost exclusively in midline cysts, and most commonly communicates to the posterior fossa.6Conversely, intracranial dermoid cysts in the posterior fossa may communicate to a posterior scalp nodule via a sinus tract. Serious complications such as infections, aseptic meningitis, and mass effect are associated with the latter condition.7
Heterotopic brain tissue is a sequestrated rest of brain or meninges most commonly located on the occipital or parietal area of the scalp.8It presents similarly to cephaloceles, including a hair collar sign, but lacks intracranial communication.
In contrast to a scalp nodule, ACC is a congenital absence of skin that most commonly presents as a small area of ulceration or full-thickness skin loss on the vertex scalp. Larger ACC lesions are more commonly associated with underlying defects in the skull or meninges,9and 20% of vertex ACCs will have an associated underlying bone defect.10They may also present with a hair collar sign.4
The patient presented with a pink, hairless, glistening scalp nodule that expanded with maturity. The lesion was atypical for more common entities such as hemangioma, port-wine stain, ACC, or sebaceous nevus.
This case emphasizes that congenital scalp midline lesions are associated intracranial communication. Nodules in the midline that fluctuate with activity, have an overlying dimple, or have a hair collar sign are particularly concerning. High-risk lesions of ACC are often larger, irregularly shaped, and situated on the cranial vertex.11These features warrant a thorough physical examination, neurological examination, magnetic resonance imaging,12and usually a neurological surgery consult. Identification is critical as delayed diagnosis is associated with a higher incidence of neurological complications.13This patient's scalp nodule at the posterior midline prompted investigation and emphasizes that regardless of age or symptoms at presentation, a midline scalp lesion deserves medical attention.
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Correspondence:Maria Garzon, MD, Department of Dermatology, Herbert Irving Pavilion, 12th Floor, 161 Fort Washington Ave, New York, NY 10032 (firstname.lastname@example.org).
Accepted for Publication:December 16, 2009.
Author Contributions:Study concept and design: Daly, Barnett, and Garzon. Acquisition of data: Daly and Garzon. Analysis and interpretation of data: Feldstein and Garzon. Drafting of the manuscript: Daly and Garzon. Critical revision of the manuscript for important intellectual content: Barnett, Feldstein, and Garzon. Study supervision: Barnett, Feldstein, and Garzon.
Financial Disclosure:None reported.
Picture of the Month—Diagnosis. Arch Pediatr Adolesc Med. 2010;164(6):578. doi:10.1001/archpediatrics.2010.68-b