Year : 2010 | Volume
: 53 | Issue : 3 | Page : 560--561
Glial heterotopia of the scalp
YK Inchara1, T Rajalakshmi1, Kanishka Das2,
1 Department of Pathology, St. John's Medical College and Hospital, Bangalore - 560 034, India
2 Department of Paediatric Surgery, St. John's Medical College and Hospital, Bangalore - 560 034, India
Y K Inchara
Department of Pathology, St. John«SQ»s Medical College, Bangalore - 560 034
|How to cite this article:|
Inchara Y K, Rajalakshmi T, Das K. Glial heterotopia of the scalp.Indian J Pathol Microbiol 2010;53:560-561
|How to cite this URL:|
Inchara Y K, Rajalakshmi T, Das K. Glial heterotopia of the scalp. Indian J Pathol Microbiol [serial online] 2010 [cited 2021 Nov 30 ];53:560-561
Available from: https://www.ijpmonline.org/text.asp?2010/53/3/560/68273
Scalp masses in children have a varied etiology. While many are associated with pathognomonic signs (e.g., the punctum of a sebaceous cyst) and can be convincingly diagnosed clinically, a few are histological surprises even to the astute clinician. A midline scalp mass in a 5-year-old that was clinically mistaken for a typical dermoid but finally diagnosed to be a glial heterotopic nodule is presented.
A 5-year-old girl presented with a 5 Χ 4 cm painless nodule in the posterior midline of the scalp. Noticed since birth, it was progressively increasing in size proportionate to the somatic growth of the child. At physical examination, there was a nontender, soft, noncompressible mass at the parieto-occipital junction [Figure 1]. There was no cough impulse and an underlying bony defect was not evident. A magnetic resonance imaging showed the lesion to be a midline, well-circumscribed, heterogenous, mixed intensity mass in the posterior parieto-occipital junction. It was predominantly extracranial with a thin stalk extending across the cranial vault through a narrow defect. The underlying intracranial structures were normal and separate from the extracranial mass lesion [Figure 2]. A differential diagnosis of a dermoid or an atretic encephalocele was entertained. At surgery, the encapsulated mass was excised with an ellipse of the overlying skin. The base of the mass showed a 2 mm stalk leading intracranially through a defect in the bony vault. There was no meningeal investment and no duraplasty was required. The stalk was severed and the scalp defect closed after appropriate mobilization.
Macroscopically, the lesion was firm, nodular, covered by skin on the superficial aspect and had a grey-white cutsurface. On microscopy, the deep dermis showed a well-circumscribed lesion composed of mature glial tissue [Figure 3]a with a few small, abortive ependymal canals [Figure 3]b. Foci of calcification were evident. The periphery of the lesion showed thickened fibrous elements and numerous dendritic melanocytes [Figure 3]c. Neither neurons nor ganglion cells were identified. The overlying epidermis was attenuated with the absence of appendages. The rest of the dermis showed a mild chronic inflammatory cell infiltrate and melanophages. These features confirmed the diagnosis of a glial heterotopia (GH). At 1 year follow-up, the child is well, asymptomatic and there is no residuum or recurrence.
The term "heterotopic brain tissue" was first introduced by Lee and McLaurin  in 1955 to encompass lesions containing glial tissue with or without meninges and having no connection with the central nervous system. GH is extremely rare, with a mere 13 well-documented cases in English literature. Usually these lesions are present at birth as bald, painless, soft nodules that proportionately increase with the growth of the child. Sometimes these bald nodules may be surrounded by a circle of long coarse hair (hair collar sign) and accompanied by a capillary stain.  The absence of a meningeal investment and an obvious intracranial communication distinguishes it from a typical encephalocele.  Yet, the described case had numerous melanocytes at the periphery of the lesion. As melanocytes are physiologically present on leptomeninges, this finding suggests the presence of rudimentary meningeal tissue.
The exact pathogenesis of these lesions is unknown, although several hypothetical etiopathogenetic mechanisms have been postulated. These include a sequestrated encephalocele, extracranial separation of embryonic neuroglia and displacement of neuroectodermal cells during early embryogenesis with potential for differentiation. , The first theory seems to be the most probable since both encephaloceles and heterotopias mostly occur in the occipital regions. Although most of the reported cases claim an absence of an underlying bone defect, Lee and McLaurin  have emphasized that the "central meningeal stalk seen in their case may have penetrated the cranium through a passage so small that it may have been overlooked." The communicating stalk may contain fatty or meningeal tissue too. Zook et al. have described a case where an external dimple was perceived in the cranium underlying the tumor, suggesting an erstwhile embryonic connection that had later obliterated. This case had features similar to that described by Lee and McLaurin  and supports the contention that GH of the scalp is a variant of encephalocele.
In conclusion, GH of the scalp is an important although rare entity in the differential diagnosis of scalp nodules in children and appropriate preoperative imaging is essential to exclude an associated intracranial component.  The surgical management is accordingly tailored to a simple excision or an additional limited craniectomy to achieve complete extirpation. Histopathological examination is confirmatory and the prognosis after complete excision is excellent.
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