Definition: Pericallosal lipoma is a fatty tumor of the corpus callosum that can extend to the choroidal areas.
Incidence: Found in one of 0.04-0.4:10,000 autopsies.
Etiology: The pathogenesis of a pericallosal lipoma is considered to be the result of an abnormal resorption of the primitive meninges. Usually, this resorption occurs between the eighth and the 10th week of development. When the primitive meninge persists longer, instead of being resorbed, it differentiates into lipomatous tissue. Such lipoma may develop in all the cerebral cisternae, but they are much more frequent in the area of the corpus callosum where it interferes with its normal growth between the 11th and 20th weeks. Therefore, anomalies of the development of the corpus callosum (complete or partial agenesis, hypoplasia) almost always coexist. The degree of anomaly seems to be in relation with the size and location of the lipoma.
Diagnosis: Easily found in all patients with this anomaly.
Two morphologic types of pericallosal lipoma have been described on the basis of MR imaging findings in adults and children:
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One is a tubulo-nodular type, appearing round and measuring >2 cm. It is usually anterior and associated with extensive callosal and possibly fronto-facial anomalies.
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The second type is curvilinear: thin, elongated, measuring <1 cm in diameter and usually more posterior. The corpus callosum is only mildly hypoplastic. The tubulo-nodular type is much more common.
On obstetric sonograms, the lipoma is best visualized on an image obtained slightly above the image that is intended to measure the biparietal diameter. The aspect of a pericallosal lipoma is characteristic: a nodular or curvilinear mass within the interhemispheric fissure. A lipoma is always an echogenic mass. The echogenicity of the lipoma is very similar to that of the parietal bone. The margins are smooth but can be irregular and somewhat spiculated in larger tumors. They can extend towards the frontal lobes and/or towards the choroid plexuses.
The diagnosis of the tubulo-nodular type is easier than the diagnosis of the curvilinear type. Fetal MR imaging may help for the evaluation of the associated anomalies, especially of the frequent callosal anomaly, since he morphology and integrity of the underlying corpus callosum is harder to assess by using sonography.
Fetal MR imaging has been recently performed to further asses this cases in utero. It can confirm the presence of the lipoma (can characterize very well fatty tissue) and also characterize the morphology of the corpus callosum in all cases; it can show the extension of the lipoma in a much better and detailed way than the conventional ultrasound.
Genetic anomalies: Unknown.
Differential diagnosis:
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Hemorrhages
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Teratoma
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Craniopharingioma.
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Primitive neuroectodermal tumors
Less likely, but also in the differential diagnosis list are:
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Glioblastoma multiform
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Medulloblastoma
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Gliomas of the optic bulbs and of the hypothalamus
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Metastasis of choriocarcinoma
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Astrocytoma
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Fetus-in-fetu.
Assdociated anomalies:
The entity is rarely isolated, and the fetal anatomical survey must be as complete as possible to detect all associated malformations.
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Dysgenesis/agenesis of the corpus callosum and gyration anomalies. Some authors have suggested that these lipomas may be part of specific malformative syndromes.
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Goldenhar syndrome.
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Trisomies 13, 15, 18, and 21
Prognosis.
Very good prognosis for fetuses with isolated lipoma of the corpus callosum, with normal results in neurological examinations in most of the series. If other anomalies are encountered, the prognosis is variable. Fifty percent of the interhemispheric lipomas are associated with seizures starting in the second decade of life. Mental retardation and psychological disorders may develop later in life.
Management:
Aside from fetal karyotyping, advisable because of the reported association with aneuploidy, standart prenatal care and delivery should not be altered.
MRI Imaging to complement prenatal sonographic findings is mandatory.
Concerning the tumors growth, little is known. We know fat cells markedly increase in size during infancy. It has been shown that growth of intraspinal lipoma may parallel the postnatal fatty growth of the patients and that, conversely, a diet leading to a reduction of the body fat may determine a decrease in the size of the spinal lipoma. Therefore, it is suggested that patients with intraspinal lipomas be followed up throughout childhood and that their weight be monitored. The same could likely apply to intracranial lipomas; however, this postnatal growth has not been reported until now.
References:
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