When Fat Meets the Brain: Corpus Callosum Lipoma in a Neonate

Abstract

Lipoma of the corpus callosum is a rare congenital malformation of the central nervous system and is seldom encountered in clinical practice. These lesions are most often discovered incidentally during neuroimaging performed for unrelated clinical indications. We report the case of a male neonate presenting with transient hypotonia, in whom a congenital lipoma of the corpus callosum was identified on imaging. The diagnosis was established using cranial ultrasonography followed by magnetic resonance imaging. The clinical course was favorable, with spontaneous resolution of hypotonia under conservative management. This case highlights the role of ultrasound and MRI in the diagnosis of congenital intracranial lipomas and the typically benign course of isolated corpus callosum lipomas.

Introduction

Lipoma of the corpus callosum is a rare congenital lesion resulting from abnormal persistence of mesenchymal tissue during embryogenesis. It accounts for less than 0.1% of all intracranial tumors and is typically found along the midline structures of the brain. ¹ The condition was first described by Rokitansky in 1856, and remains an uncommon developmental malformation rather than a true neoplasm. ²

These lesions are composed of mature adipose tissue and are often associated with agenesis or dysgenesis of the corpus callosum.^3,4 Most are asymptomatic and discovered incidentally during imaging studies performed for other conditions. When symptoms occur, they are usually related to associated brain malformations rather than the lipoma itself. ⁵

Imaging plays a central role in diagnosis. In neonates, cranial ultrasound is often used as a first-line modality and may demonstrate a midline echogenic lesion. Magnetic resonance imaging (MRI) is the modality of choice for definitive diagnosis, allowing accurate tissue characterization, confirmation of fat content using fat-suppressed sequences, and detailed assessment of associated cerebral anomalies, without exposure to ionizing radiation.

We present a case of a neonate with a congenital lipoma of the corpus callosum, diagnosed incidentally during evaluation for neonatal hypotonia, emphasizing the contribution of ultrasound followed by MRI in establishing the diagnosis.

Case Description

A male neonate was born at 38 weeks of gestation by cesarean section after an uneventful pregnancy. Apgar scores were 8 and 9 at 1 and 5 minutes, respectively. Generalized hypotonia was noted within the first 48 hours of life and persisted for several days, associated with diminished primitive reflexes. There was no family history of neurological or metabolic disorders.

Initial biological investigations, including blood glucose levels, arterial blood gases, serum electrolytes, and inflammatory markers, were within normal limits, with no evidence of hypoxic–ischemic injury or metabolic disorder.

Given the presence of persistent neonatal hypotonia with normal biological parameters, a structured stepwise diagnostic approach was initiated to identify a potential central nervous system cause. The first diagnostic consideration included hypoxic–ischemic encephalopathy; however, the absence of perinatal distress, normal Apgar scores, and normal laboratory findings made this diagnosis unlikely. Metabolic and infectious etiologies were also considered but were excluded based on normal metabolic screening and inflammatory markers.

As part of the initial workup for neonatal hypotonia, a cranial ultrasound was obtained to rule out hypoxic–ischemic injury. The examination revealed a homogeneous, well-defined hyperechoic structure along the midline, following the expected course of the corpus callosum (Figure 1). At this stage, the differential diagnoses included intracranial hemorrhage, calcified lesions, intracranial tumors, and fat-containing congenital malformations. The sharply delineated margins and marked hyperechogenicity were atypical for hemorrhage and raised suspicion for a lipomatous lesion, prompting further evaluation with MRI.

Figure 1.

Cranial ultrasound images in axial (A) and sagittal (B) planes showing a well-defined, homogeneous hyperechoic lesion along the midline (arrows), following the contour of the corpus callosum, consistent with a lipomatous lesion.

The lesion appeared hyperintense on both T1- and T2-weighted sequences, showed complete signal suppression on fat-saturated sequences, and demonstrated no enhancement after gadolinium administration. No restricted diffusion was observed. These MRI characteristics allowed exclusion of other differential diagnoses such as dermoid cysts, teratomas, and neoplastic lesions, which typically show heterogeneous signal intensity, incomplete fat suppression, or contrast enhancement. The corpus callosum was intact and normally formed, and no other brain malformations were identified. These imaging findings confirmed the diagnosis of a congenital lipoma of the corpus callosum of the curvilinear posterior type, with posterior calcifications (Figure 2).

Figure 2.

(A) Coronal T2-weighted MRI image demonstrating a homogeneous hyperintense lesion along the midline corresponding to the corpus callosum (arrow). (B) Sagittal T2-weighted MRI image confirming a linear, hyperintense lesion following the contour of the corpus callosum (arrow). (C) Sagittal T1-weighted MRI image showing a markedly hyperintense signal consistent with fat (arrow). (D) Axial T1-weighted MRI image illustrating a high signal intensity lesion within the pericallosal region (arrow).

Given the absence of hydrocephalus, seizures, or mass effect, a conservative approach was adopted. The patient was managed with clinical monitoring and neurological follow-up. No medical or surgical intervention was required, as the lesion showed no signs of progression or associated complications. A pediatric neurology consultation was obtained, which confirmed the absence of focal neurological deficits or epileptic manifestations. Supportive care was provided, including close monitoring of feeding, muscle tone, and spontaneous motor activity during hospitalization.

At 3 months, the infant showed normal growth and improvement in muscle tone, with no new neurological symptoms. Neurological examination at follow-up revealed age-appropriate motor development and normal primitive reflexes. No seizures, feeding difficulties, or signs of increased intracranial pressure were observed. Ongoing clinical follow-up was recommended, with imaging reserved for the emergence of new neurological symptoms.

Methods

This manuscript reports a single clinical case. Clinical, laboratory, and imaging data were retrospectively collected from the patient’s medical records.

Ethical Approval and Informed Consent

This case report was reviewed by the Ethical Committee for Biomedical Research (CERB) of the Faculty of Medicine and Pharmacy of Rabat. Formal ethical approval was not required, as this report involved retrospective clinical observation without experimental intervention or identifiable patient data, in accordance with institutional guidelines. Written informed consent for publication of clinical information and non-identifiable imaging data was obtained from the patient’s parents.

Discussion

Lipoma of the corpus callosum is a developmental malformation rather than a true neoplasm. It arises from abnormal persistence and differentiation of the primitive meninx, a mesenchymal derivative of the neural crest that normally resorbs between the 8th and 10th week of gestation.^1,3 When this process fails, the residual mesenchyme differentiates into mature adipose tissue, forming a lipoma along the interhemispheric fissure. ⁴

Although its exact incidence is unknown, callosal lipoma represents less than 0.1% of all intracranial tumors. ² The pericallosal region is the most common location, accounting for nearly half of all intracranial lipomas. ⁵ Two morphologic types have been described: the tubulonodular type, which is larger (>2 cm), usually anterior, and frequently associated with callosal agenesis; and the curvilinear type, which is thin, and follows the contour of the corpus callosum.^6,7 The latter type, as observed in our patient, is typically posterior, asymptomatic, and rarely associated with additional brain malformations.

No specific maternal or fetal risk factors have been consistently identified. Corpus callosum lipomas are generally considered sporadic developmental anomalies, with most cases occurring in the absence of maternal infection, teratogenic exposure, metabolic disease, or known genetic syndromes, as in the present case.

Clinical manifestations depend mainly on associated abnormalities rather than the lipoma itself. Many patients remain asymptomatic throughout life. ⁸ In neonates, however, nonspecific findings such as hypotonia, developmental delay, or seizures may prompt neuroimaging and lead to incidental diagnosis.

In the present case, hypotonia was the initial clinical sign that prompted neuroimaging. However, no structural brain abnormalities, metabolic disorders, or hypoxic–ischemic injury were identified. MRI demonstrated an isolated corpus callosum lipoma without mass effect or associated malformations. The hypotonia resolved spontaneously during follow-up without specific treatment. Therefore, the initial symptoms were considered nonspecific and unrelated to the lipoma, most consistent with transient neonatal hypotonia reflecting functional neuromuscular immaturity.

Imaging is central to diagnosis. On ultrasound, a corpus callosum lipoma typically appears as a well-defined, echogenic midline structure conforming to the expected course of the corpus callosum. MRI confirms the fatty nature of the lesion, which appears hyperintense on T1- and T2-weighted sequences, shows complete signal suppression on fat-saturated sequences, and demonstrates no enhancement after contrast administration. MRI also allows accurate evaluation of the corpus callosum and exclusion of associated cerebral anomalies.^9,10

Although CT can demonstrate a hypodense lesion with negative attenuation values consistent with fat, its use in neonates is limited by exposure to ionizing radiation and is generally unnecessary when MRI is available.

Management is mainly conservative. Surgical excision is rarely indicated due to the lesion’s close adhesion to adjacent neurovascular structures and the risk of significant complications. Management focuses on treating associated symptoms such as seizures when present. In isolated corpus callosum lipomas diagnosed by ultrasound and MRI, no specific treatment is required, and the prognosis is excellent. ¹⁰

Conclusion

Congenital lipoma of the corpus callosum is a rare developmental anomaly that may occasionally be detected in neonates evaluated for nonspecific neurological signs. most often as an incidental finding. Ultrasound especially MRI, is essential for accurate diagnosis and to exclude associated malformations without exposure to ionizing radiation. Most cases require no intervention, and in isolated forms, the long-term neurological prognosis is excellent.