Cutaneous Ectopic Brain
Updated: Jun 16, 2022
Author: Camila K Janniger, MD; Chief Editor: Dirk M Elston, MD
Overview
Practice Essentials
Extracranial brain tissue without a direct connection to the brain itself may be an isolated cutaneous embryonic defect, usually on occipital or parietal areas of the scalp. It is also known as heterotopic brain tissue or cutaneous ectopic brain (CEB). Ectopic brain tissue may appear elsewhere too, such as in the trigeminal nerve to produce rapid-onset trigeminal neuralgia.[1] Ectopic olfactory and taste receptors may also occur, transmitting signals to the brain.[2]
Lee and Mclaurin[3] described CEB in 1955 in a 1-year-old girl with a flat, almost perfectly circular, bluish-red plaque approximately 3 cm in diameter on the posterior midline of her scalp. Microscopically, heterotopic glial tissue in a pattern suggestive of abortive gyri and sulci was evident within the dermis. Additional patients with CEB have since been described.
Heterotopic brain tissue is a rare developmental abnormality that usually has no effect on neurological development.
Pathophysiology
Cutaneous ectopic brain (CEB) may be an isolated embryonic rest or a congenital herniation through the skull with an eventual loss of connection. Perhaps the neural tube initially overgrows, preventing closure of the cranial or spinal coverings. Thus, its pathogenesis is uncertain.
Etiology
The cause is unknown. Cutaneous ectopic brain (CEB) may be an isolated embryonic rest or a congenital herniation through the skull with an eventual loss of connection.
Prognosis
The prognosis for patients with cutaneous ectopic brain (CEB) generally is good because no communication exists with underlying structures and few, if any, serious associated anomalies occur.
Diagnostics
See Workup.
Treatment
Cutaneous ectopic brain (CEB) can be treated with complete excision. Perform a complete evaluation, including possible ultrasound, cranial tomograms, and consultation with a neurosurgeon, prior to surgery.
Epidemiology
Many congenital cutaneous disorders of the scalp have been described, all of which are quite uncommon. Cutaneous ectopic brain (CEB) is less common than encephalocele.[4]
Presentation
History
Parents or physicians usually notice a cystic nodule at birth or shortly thereafter. A retrospectively review of the demographic, clinical, and histopathologic records of 11 infants with 12 heterotopic neural nodules of the scalp showed all lesions were located in the parietal or occipital region.[5] All but one had overlying alopecia surrounded by a ring of long, coarse hair (the hair collar sign), and 9 of 11 children had a capillary stain surrounding the lesion. Careful clinical evaluation and MRI of the brain should be performed prior to biopsy or excision of these scalp lesions.[6]
Heterotopic brain tissue is most often seen in the nasal region; other locations for ectopic brain tissue are less common, with a few observations on the face or neck.[7] Heterotopic brain tissue is rarely seen in the orbit. Orbital ectopic glial and glioneuronal brain tissue has been described.[8, 9] Heterotopic brain tissue has also been described in a cleft palate; this is a rare developmental anomaly.[10] Progressive proptosis in a neonate was described as a result of an ectopic cerebral rest in the orbit in the absence of a formed eye.[11]
Physical Examination
Cutaneous ectopic brain (CEB) is usually seen at birth as a 2-4 cm diameter, solitary, circular, bald scalp plaque or cyst, which may be compressible.
The plaque or cyst may be the color of skin, erythematous, or bluish, and tends to be on the midline occipital or parietal scalp.
A collar of hypertrophic hair may be evident surrounding the plaque or cyst (the hair collar sign[12, 13] ). A cutaneous marker for neural tube closure defects of the scalp (hair collar sign) consists of a ring of long, dark, coarse hair surrounding a midline scalp nodule. This sign should alert the physician to the possibility of ectopic neural tissue in the scalp or underlying central nervous system malformations.
Complications
Caution is obligatory because skin biopsy or needle aspiration might lead to retrograde infection should the lesion communicate with the brain. If a congenital defect overlies a large blood vessel such as the sagittal sinus, removal of what appears to be a crust of dried serum may produce a fatal hemorrhage.
DDx
Diagnostic Considerations
See the list below:
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Encephalocele[14]
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Meningocele
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Cutaneous ectopic meningioma (psammoma)[15, 16, 17]
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Neurofibroma
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Porokeratosis of Mibelli
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Triangular alopecia
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Nevus sebaceus of Jadassohn
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Aplasia cutis congenita: Alopecia overlying cutaneous ectopic brain may suggest this diagnosis.
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Hemangioma
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Lymphangioma
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Cephalohematoma
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Melanotic progonoma
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Myxopapillary ependymoma (possibly)
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Ectopic orbital meningoma, which may be evident as a medial canthal mass[18]
The prominent collarette of hair that may be seen in persons with cutaneous ectopic brain (CEB) may also be seen in other neurocutaneous disorders (eg, encephalocele, cutaneous meningioma).[4, 19] Consider the possibility of a dermal sinus or a direct connection to the meninges or central nervous system when assessing congenital defects.
Encephaloceles are usually in the midline scalp, either hairless or with a collarette of hair. The nasal glioma, similar to CEB, may have no connection to underlying central nervous system structures. It appears on the nose as a smooth, often polypoid tumor. Cutaneous heterotopic meningeal nodules (cutaneous meningiomas) are seen most often at birth or in childhood as small subcutaneous fibrous nodules.[20] Primary ectopic meningioma may also occur on the tongue.[21]
Cutaneous meningiomas may also require distinction.[20]
Heterotopic CNS tissue may also occur in the form of an ethmoidal polyp. One should distinguish these from meningoencephalocele, as the latter have an anatomical connection with central nervous system tissue. Contrast-enhanced imaging is essential to show no connections with intracranial tissue.[22]
Glial heterotopia or ectopic brain may appear as a dacryocystocele.[23]
Differential Diagnoses
Workup
Imaging Studies
In cutaneous ectopic brain (CEB), evaluate any bald scalp plaque or nodule with suitable noninvasive diagnostic techniques (eg, ultrasound, cranial tomograms), with input from a neurosurgeon.
Preoperative imaging may identify calvarial defects.[5] Preoperative imaging is essential to document possible intracranial involvement and to reduce the risk of penetration of the dura during resection.
Brain heterotopia may be evident on MRIs and positron-emission tomography (PET) scan images. Heterotopia may demonstrate normal or increased fluorodeoxyglucose uptake on PET scan images, sometimes confusing matters when other pathologies are being considered.[24]
Procedures
Caution is obligatory because skin biopsy or needle aspiration might lead to retrograde infection should the lesion communicate with the brain.[5]
If a congenital defect overlies a large blood vessel such as the sagittal sinus, removal of what appears to be a crust of dried serum may produce a fatal hemorrhage.
Histologic Findings
The overlying epidermis in CEB is normal or somewhat atrophic because of the ectopic brain tissue impinging upon it. Brain tissue may be noted consisting of a small nodule of predominant eosinophilic fibrillary stroma, containing astrocytes, oligodendrocytes, and neurones.[25] The dermis has an island of malformed brain tissue composed of glial cells and some neurons in a pattern that may suggest abortive gyri and sulci. Vascular leptomeninges and fibrous bands, possibly representing dura, may envelop this brain tissue. Many hair follicles and sweat glands may be evident.
Histologic examination may show neural tissue staining with S-100 protein and glial fibrillary acid protein, but not with a neurofilament stain, suggesting glial cell origin.