Intracranial lipoma exists in
Case 125
【Progress】Our neurosurgeon introduced him to university hospital for consulting about whether he needs follow-up observation or surgical resection of the lipoma. As a result, he was concluded to have no treatment and come to us if re-convulsion emerged.
【Discussion】
When lipoma emerges in the body, it is easy to consider that lipoma is originated from adipose tissue, one of the components of the soft tissue of the body. However, how about in the brain, there is no adipose tissue in the brain and its covering. Although several hypotheses were listed, the most accepted hypothesis of emerging intracranial lipoma is abnormal persistence and mal-differentiation of meninx primitive (1, 2). In short, intracranial lipoma results from congenital anomaly rather than neoplasm. Meninx creates the covering materials of dura mater, arachnoid and pia mater, resulting in playing a role of producing arachnoid space and cistern. It is reported that meninx first creates pre-pontomedullary cistern and then creates much subarachnoid space accompanied by dissolution of meninx (1). Meninx proceeds to create superior cerebral cistern and suprasellar cistern lately and the latest area of resorption is along the area of the lamina terminalis. Meninx resolution is completed in 2 months (1, 2). Therefore, the large opportunity of meninx mal-differentiation occurs in the late formation of cistern. In fact, the distribution of intracranial lipoma correlates with the pattern of cistern formation and dissolution of meninx: 36% peri-callosal, 25% quadrigeminal, 11% suprasellar, 7% cerebellar-pontine (2-4). The persistent meninx and/or maldistribution of lipoma is considered to interfere with normal growth of adjacent neural tissue. The peri-callosal lipoma is reported to combine with agenesis or hypoplasia of corpus callosum (5, 6).
In our case, MRI and CT showed intracranial lipoma in the midline of hemisphere, peri-corpus callosum (Figs.1-5) and in the lateral ventricle (Figs.1-4) with hypoplasia of corpus callosum (Figs.1A, 2C, 5B, 5C).
Corpus callosum is a bridge of neural information between right and left hemispheres. It is formed in 3-4 months of fetus (5, 6). It is possible that lipoma formation precedes corpus callosum formation because meninx resolution occurs in 2 months of fetus (1, 2). It is reported that lipoma formation occurs between 3-4 months after gestation, taking place resolution of meninx (2, 5, 6). Agenesis or hypoplasia of corpus callosum generates epilepsy in 23-39% (5, 6). The mechanism of epilepsy is unclarified. Although corpus callosum is not a causative for seizure (cortical abnormality is a causative), it is a main pathway of seizure generalization. Especially, genu of corpus callosum is reported to be a major pathway of general epilepsy, while splenium is related to partial epilepsy (7). When epilepsy is resistant to drugs, callostomy is conducted to prevent seizures.
As treatment for intracranial lipoma, surgical excision is not recommended, sometimes contraindicative due to the strong adhesion to the surrounding tissue and highly vascular nature (7). In our case, MRI with T2* showed lipoma was surrounded by small vessels (Fig. 3B), implying massive hemorrhage if surgical resection were attempted. MRI with DWI & ADC is meaningless for differentiating from hemorrhage or malignancy because DWI b0 and b1000 are basically using echo planer with fat suppression, leading to that lipoma is low signal on both DWI b0 and b1000. ADC equals to the slope of the curve using the acquired signal intensity values of b0 and b1000 or b2000 (ADC = Loge Sb/Sb0)(2). Then, when we confirm the low signal intensity in the lesion of area of interest, we had better not see ADC map (8).
【Summary】
We present a thirty one-year-old male who experienced convulsion. Brain MRI and CT showed lipoma in the peri-callosal area and in the lateral ventricle and hypoplasia of corpus callosum. MRI with T2* showed rich vascular network surrounding the lipoma. We should keep in mind that intracranial lipoma is congenital anomaly rather than neoplasm. It is widely accepted that intracranial lipoma comes from mal-differentiation of meninx that originally forms arachnoid space by production of dura, meninge and pia mater. Meninx creates first pre-pontomedullary cistern lately followed by superior sagittal sinus cistern and finally by lamina terminalis, that indicates lipoma can occur in any place of arachnoid space. Cortical anomaly is a causative of epilepsy and corpus callosum is a main pathway of epilepsy generalization. Hypoplasia or agenesis of corpus callosum causes epilepsy. Although its mechanism is not clarified, electric transmit disorder might easily cause cortex excitement. DWI and ADC map is less valuable to check lipoma simply because DWI b0 and b1000 are basically using echo planer with fat suppression, implying lipoma is low signal on both DWI b0 and b1000. Then, ADC calculation is difficult because DWIb0 is approaching to 0.
【References】
1.Osaka K, et al. Development of cerebrospinal fluid pathways in the normal and abnormal human embryos. Child's Brain 6:26–38, 1980.
2.Truwit CL, Barkovich AJ. Pathogenesis of intracranial lipoma: An MR study in 42 patients. AJR Am J Roentgenol 1990;155:855-64.
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5.Taglialatela G, et al. Lipomas of corpus callosum. Neuroanatomy 2009;8:39-42.
6.Maiuri F, Cirillo S, Simonetti L et-al. Intracranial lipomas. Diagnostic and therapeutic considerations. J Neurosurg Sci. 1989;32 (4): 161-7.
7.Wieshmann UC, et al. The role of the corpus callosum in seizure spread: MRI lesion mapping in oligodendrogliomas. Epilepsy Res. 2015 Jan;109:126-33.
8.Kita M. Personal communication in Fuchu Hospital
2018.10.17