Hypothalamic Lipoma: Outcome of an Intracranial Developmental Lesion

Background Hypothalamic lipomas are benign developmental lesions that tend to be discovered incidentally. This article describes the radiological features, outcome, and the postulated theories behind hypothalamic lipomas development. Methods The electronic archive of neurosurgery was retrospectively reviewed. All patients with a neuroradiological diagnosis of hypothalamic lipoma, between 2005 and 2020, were included. Results Out of 246 patients with intracranial lipomas, a total of six patients with hypothalamic lipomas have been identified. On computed tomography images, one of the hypothalamic lipomas demonstrated calcification. On magnetic resonance imaging, peripheral enhancement after contrast administration was noted in one of the lesions. Considering the benign nature of the lesions, neurosurgical intervention was not indicated. Conclusion The majority of patients with hypothalamic lipomas are asymptomatic and undergo brain imaging for other indications. Although uncommon, such developmental lesions can be identified in the general population, especially with the advancement of neuroimaging techniques.


Introduction
Intracranial lipomas are uncommon benign lesions comprising less than 1% of intracranial tumors [1][2][3]. They are commonly located in the midline and associated with midline brain deformities [4]. Intracranial lipomas have been proposed to be secondary to proliferation of normal adipose cells present in the leptomeninx, deposition of fats as products of neuronal tissue, or persistence of displaced dermal anlage that later forms the lipoma within the neural tube [3]. Another theory proposed that intracranial lipomas are due to the persistence of mesenchymal tissue that gives rise to the meninges "meninx primitiva" which is thought to be a derivative of the neural crest [3]. Intracranial lipomas are usually asymptomatic and do not necessitate treatment [3]. Surgical intervention is preserved for patients with neurological deficits [5] The incidental finding of intracranial lipomas is uncommon. Considering their poor discussion in the literature, the present article outlines the radiological findings and outcome of hypothalamic lipoma.

Methods
The radiological and departmental database of neurosurgical patients were reviewed from the period of 2005-2020. A

Ethical Considerations
Patients' identities were concealed. All radiological images were anonymized. The study was noninterventional and retrospective in nature.

Results
Of 246 patients with intracranial lipomas, a total of six patients with hypothalamic lipomas of variable imaging appearances have been identified from the period of 2005-2020. The youngest patient was 16 years old (age range = 16 − 60 years) at the time of diagnosis. The mean age of all patients was 33:5 ± 13:56 years. There was no gender predilection (males; N = 3, females; N = 3). All patients had no signs or symptoms of endocrinopathy. Calcification and peripheral enhancement after contrast demonstration were noted in two patients with hypothalamic lipoma. Table 1 outlines the characteristics of patients with hypothalamic lipoma in the present case series.

Patient 1.
A 27-year-old male, known to have asthma, dextrocardia, hypertension, and hyperthyroidism, presented to the neurosurgery outpatient clinic due to intermittent episodes of mild-intensity headache. The headache was mainly triggered by exposure to allergens during certain seasonal times of the year. The patient reported no history of vomiting, seizures, loss of consciousness, dizziness, facial pain/ swelling, recent ear infection, postnasal drip, gross obesity, history of precocious puberty, blurry vision, or any other associated symptoms suggestive of high intracranial pressure. In the clinic, the patient's physical examination revealed that he was alert and oriented to person, place, and time with a Glasgow Coma Scale (GCS) of 15/15. Pupils were 3 mm bilaterally reactive to light with no gaze preference. The remainder of the physical examination was grossly intact. Computed tomography (CT) scan revealed a homogeneously fat-containing lesion in the hypothalamus (Figure 1(a)). Magnetic resonance imaging (MRI) without and with contrast showed a stable, small (10 mm) hypothalamic lipoma with no pathological enhancement (Figures 1(b)-1(d)).

Patient 2.
A 60-year-old female, known to have diabetes, coronary artery disease, hypothyroidism, dyslipidemia, and cholelithiasis, was referred from the emergency department to ophthalmology clinic due to progressive decrease in visual acuity. Physical examination was grossly intact. A nonenhanced brain computed tomography revealed a hypodense lesion with a predominant fatty component and a focus of calcification ( Figure 2). The patient was referred to neurosurgery clinic for further assessment. However, she did not show up to her neurosurgery or ophthalmology appointments since her initial ophthalmological assessment.

Patient 3.
A 16-year-old male, not known to have any medical illness, presented to the emergency department due to episodic vasovagal syncope after the sight of blood.
There was no history of headache, dizziness, abnormal movements, or seizures. Neurological examination was intact. A brain MRI revealed a hypothalamic lipoma (Figure 3).

Patient 4.
A 26-year-old female, known to have epilepsy diagnosed at the age of 18 years, presented with bilateral myoclonic abnormal jerky movements involving the upper limbs for five minutes. Afterward, the abnormal movements secondarily generalized to involve all limbs for a total of ten minutes. Physical examination, after recovery from the seizure event, was grossly intact. A brain MRI, utilizing epilepsy protocol, revealed a small hypothalamic lipoma (Figure 4).

Patient 5.
A 36-year-old male, not known to have any medical illness, was complaining of intermittent band-like headache. The headache was associated with nausea and dizziness. Physical examination was grossly intact. Brain CT scan revealed an incidental hypothalamic lipoma ( Figure 5).

Patient 6.
A 36-year-old female, not known to have any medical illness, presented to the emergency department complaining of moderate-intensity headache. Physical  Case Reports in Surgery examination did not reveal any deficits. Brain CT demonstrated a hypothalamic lipoma ( Figure 6).

Discussion
Hypothalamic lipomas in the adult and pediatric populations are rare. A review of the literature revealed few reported cases. We hereby report a retrospective review comprising six patients with incidental hypothalamic lipomas who were identified at our medical institute. As far as the embryologic concepts are concerned, hypothalamic lipomas are neither hamartomas nor neoplasms [6]. Rather, they develop due to congenital malformations [6]. Lipomas can be secondarily ossified, leading to the development of osteolipomas [6]. These lesions commonly tend to consist of mature adipose tissues and bony elements [6].
Hypothalamic lipomas are typically asymptomatic lesions, that is, discovered incidentally [7]. However, largesized lesions may compress adjacent structures producing focal neurological deficits [7]. Additionally, hypothalamic lipomas have been well documented to contribute to hypothalamic dysfunction, including precocious puberty, hypothermia, and obesity [8][9][10]. In the absence of endocrinological, nutritional, or genetic dysfunction, hypothalamic lipoma can be the culprit of unexplained obesity [10]. Puget et al. highlighted the importance of performing magnetic resonance imaging in patients with unexplained obesity to identify the presence of hypothalamic lipoma [10].
On neuroimaging studies, hypothalamic lipomas depict signal intensity similar to those of subcutaneous fat tissues on magnetic resonance imaging [7]. The lesions commonly demonstrate homogenous intensity without enhancement after contrast administration [7]. In rare cases, they may demonstrate a focus of superficial calcification that is best detected on computed tomography images, as shown in Figure 2 [7].
In the present case series, the diagnosis of hypothalamic lipoma was rendered after brain CT and/or MRI in all patients. The lesions were fat-suppressed in fat-saturated T2-weighted images. One of the lesions demonstrated peripheral enhancement following contrast administration. Follow-up images, in all patients, showed stable hypothalamic lipomas. Considering the benign nature of the lesions, neurosurgical intervention was not indicated. All patients had excellent outcome. Except for one patient, they are currently followed-up at the neurosurgery clinic.

Conclusion
The majority of patients with hypothalamic lipomas are asymptomatic and undergo brain imaging for other indications. The characteristic imaging features of hypothalamic lipomas on brain computed tomography and magnetic resonance imaging help narrow down the differential diagnoses in patients with hypothalamic lesions. Patients with hypothalamic lipoma are commonly managed conservatively with regular clinical and radiological follow-up. Although uncommon, such lesions can be identified in the general population, especially with the advancement of neuroimaging techniques.

Data Availability
Data is available upon request.

Ethical Approval
For this type of study, formal consent is not required. All images are anonymized. Ethical approval is exempted based on the guidelines of the research center at our institution. All the procedures being performed were part of the routine care.

Conflicts of Interest
All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements) or nonfinancial interest (such as personal or professional relationships, affiliations, knowledge, or beliefs) in the subject matter or materials discussed in this manuscript. The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.