Teaching Case

A 35-year-old female presented to our hospital complaining of left side hemianesthesia for two hours associated with dizziness and fatigue. She had a long history of seizures. On physical exam, left side hypoesthesia was detected but, she had a normal gait and normal cerebellar tests. Other findings were unremarkable.

In the quadrigeminal cistern adjacent to the Tectum, approximately 3.8x2.4x9 mm lesion with a hyperintense signal on T1 and T2-weighted MRI images was observed. The lesion was hypointense on fat-saturated T1 and SWI (due to susceptibility artefact) sequences without post-contrast enhancement, compatible with lipoma. No malformations or hydrocephalus were detected (Fig.1, 2, 3, and 4).

Intracranial lipomas are rare tumours with an incidence of about 0.1% to 0.5% of all brain tumours [1]. They are usually located on the midsagittal region mostly on the corpus callosum, quadrigeminal cistern, suprasellar, cerebellopontine angle cistern, and Sylvian cistern regions [2]. Intracranial lipomas are congenital malformations resulting from an abnormal persistence and mal-differentiation of the meninx primitive during the development of subarachnoid space [3]. Histologically these lesions show extensive adipose cells along with lipomatous hamartomas [4].

Most of the intracranial lipomas are asymptomatic and incidental findings on autopsy or neuroimaging studies for other conditions but, some are associated with congenital brain malformations, headache, vertigo, dizziness, and seizure depending on their location [1, 3]. About 20% of quadrigeminal cistern lipomas are symptomatic and their common symptoms are intracranial hypertension and hydrocephalus mostly due to mass effects, which lead to a headache. However, in the majority of cases, the cause of headache is unclear [2]. Both CT and MRI can be used for the diagnosis of intracranial lipoma but, MRI is an excellent imaging modality to accurately characterize these lesions and possible associated anomalies that can be considered more valuable than CT for such purposes [5].

The characteristic appearance of intracranial lipomas including quadrigeminal cistern lipoma on non-contrast-enhanced CT scan are fat density values ranging from -39 to -80 HU. On MRI, a hyperintense signal can be observed both on T1 and T2 weighted images. Fat suppressed images are very helpful to prove the presence of fat. After the administration of contrast medium, both on CT scan and MRI, the lesion shows no enhancement, while sometimes peripheral calcifications may be present [6].

Outcome 

Most of the intracranial lipomas are asymptomatic and require no therapy. The dense vasculature of the lipoma and its tendency to adhere to surrounding neural tissue, especially to the cranial nerves makes radical surgical extirpation technically difficult and hazardous. Therefore despite some exceptions, the risks of surgical intervention typically outweigh potential benefits [1]. 

Take-home message

The quadrigeminal cistern lipomas are rare intracranial lesions and an incidental finding on brain imaging studies. They are mostly asymptomatic and require no therapy but, sometimes may present with headache, seizures, or associated brain anomalies that need conservative treatment. The diagnosis is usually made based on imaging findings and doesn't require histologic confirmation. Thus, radiologists should be aware of these findings to establish more observatory protocols and proper differential diagnosis.