DIAGNOSIS Lipoma of the Corpus Callosum.
Intracranial lipomas are thought to be benign, slow-growing, congenital hamartomatous conditions, which are very rare . Since the original description of these tumors in 1856 by Rokitansky , approximately 200 cases have been reported . The frequency of these lesions ranges from 0.46 to 1% of all intracranial tumors . The most common location for these neoplasms is at or near the midline. In the largest study of intracranial lipomas to date, these tumors were found most frequently in the pericallosal-interhemispheric region (45%), followed by the quadrigeminal cistern (25%), and the suprasellar/interpeduncular cistern (14%) .
The diagnosis of intracranial lipoma is commonly rendered in the pediatric and young adult population, either incidentally on neuroimaging or due to the symptoms they elicit which lead to imaging studies. In older patients, intracranial lipomas are often found incidentally at autopsy. Radiographically, a lipoma of the corpus callosum is easily identified on plain skull films. Specifically, a radiolucent zone, which corresponds to the fatty tumor, is surrounded by curvilinear calcifications . MRI demonstrates a homogenous hyperintense mass on T1 weighted images and an iso- to hypointense lesion on T2 weighted images . In addition, CT scans and MRI are helpful in identifying other associated malformations.
According to Gerber et al. , fifty percent of patients with intracranial lipomas are asymptomatic. Common presenting symptoms include epilepsy, headache, behavioral changes, and cranial nerve paralysis . However, the association between epileptic seizures and intracranial lipomas remains controversial [2,3]. Gastaut et. al  reasoned that the symptomatic nature of corpus callosum lipomas is dependent on the interruption of the callosal fibers, which are replaced by the neoplasm. Such disconnection is responsible for each hemisphere to develop epileptic discharges. More specifically, EEG findings in case reports of patients with callosal lipomas and epilepsy found seizure foci located in the temporal lobe. The details of this association remain unclear .
Unfortunately in the present case we were unable to retrieve and review any EEG performed on the patient. However, we believe that the corpus callosum lipoma in this autopsy case may have been a contributing factor to the patient's history of seizures.
The precise etiology of intracranial lipomas is still a topic of discussion. Historically, theories regarding the histogenesis of these lesions include: a) hypertrophy from pre-existing fatty tissue of the meninges, b) metaplastic meningeal connective tissue, c) heterotopic malformation of dermal origin, and d) tumor-like malformation derived from primitive meninx . Another theory proposes that lipomas are midline defects due to the improper closure of the neural tube. This theory is supported by case reports in which lipomas are associated with other midline defects such as spina bifida and meningomyeloceles . The school of thought that suggests that lipomas are the result of meningeal maldifferentiation proposes that lipomas are linked genetically to other midline defects . Other features associated with the presence of intracranial lipomas include agenesis of the corpus callosum (most common), webbed toes, cleft lip, mongolism, funnel chest, facial asymmetry, high arched palate, ventricular septal defect, agenesis of the cerebellar vermis, pituitary tumors, acoustic schwannomas, and other intracranial lipomas most commonly located in the choroid plexus of the lateral ventricles . Today, intracranial lipomas are accepted to be due to the abnormal differentiation of the persistent meninx primitiva, which is a region that constitutes the inner level of the pia, arachnoid, and dura .
Macroscopically, lipomas vary in size from subcentimeter nodules to large masses. They have a bright yellow, lobulated appearance. Microscopically, lipomas consist of mature adipose tissue with varied amounts of collagen, blood vessels, and calcifications [2,5].
Anticonvulsant therapy is the treatment modality of choice in symptomatic lipomas. Surgical management proves to be challenging due to the high vascularity and adherence of the lesion to the surrounding parenchyma and should only be pursued if the patient fails medical management [2,10].
Contributed by Susanne K. Jeffus, M.D., T. David Bourne, M.D., M. Beatriz S. Lopes, M.D., Ph.D.