|Year : 2015 | Volume
| Issue : 2 | Page : 267-270
Quadrigeminal cistern lipoma: A rare case report with review of literature
Dhaval K Thakkar1, Abhijit Patil1, Dolly Thakkar2, Mansi N Jantre1, Vilasrao M Kulkarni1, Amarjit Singh1
1 Department of Radio-Diagnosis, Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth Pimpri, Pune, India
2 Department of Radio-Diagnosis, King Edward Memorial Hospital, Parel, Mumbai, Maharashtra, India
|Date of Web Publication||13-Mar-2015|
Dhaval K Thakkar
403, Alaknanda, Neelkanth Valley, Ghatkopar (East), Mumbai - 400 077, Maharashtra
Source of Support: None, Conflict of Interest: None
Two cases, one of a 6-old-year male and another of 18-year-old female with an intracranial lipoma of quadrigeminal region is reported. Intracranial lipomas usually occur in midline areas and are extremely uncommon with an incidence of 0.1% of all intracranial tumors. These were incidentally detected by computed tomography (CT) or by autopsy. Autopsy incidence of intracranial lipoma is 0.08-0.46%, while incidence of CT findings is not >0.03-0.06%. CT and magnetic resonance imaging (MRI) examination usually lead to the diagnosis, because of the very low attenuation values of lipomas on CT and the short T1 and T2 on magnetic resonance. We describe the findings of imaging studies, including CT, MRI along with a brief review of the literature.
Keywords: Blooming, gradient echo sequence, intracranial lipoma, magnetic resonance imaging, quadrigeminal lipoma
|How to cite this article:|
Thakkar DK, Patil A, Thakkar D, Jantre MN, Kulkarni VM, Singh A. Quadrigeminal cistern lipoma: A rare case report with review of literature. Med J DY Patil Univ 2015;8:267-70
| Introduction|| |
Intracranial lipomas are rare tumors with incidence of 0.1-0.5% of all intracranial tumors. , Pericallosal lipomas account for 50% of all intracranial lipomas.  The quadngeminal/superior cerebellar lipomas account for 25% of the cases followed by suprasellar/interpeduncular (14%), cerebellopontine angle (9%), and sylvian (5%) cisterns lipomas. Intracranial lipomas are uncommon intracranial neoplasms.  Lipomas are easily identified by virtue of their characteristic signals on magnetic resonance imaging (MRI) sequences, however some lipomas also do show blooming on gradient echo (GRE) which can be confused with hemorrhage.
In both of our cases, the quadrigeminal lipoma showed blooming on GRE which can be easily confused with subarachnoid hemorrhage, hence knowledge of the occurrence of lipoma in the relation to the quadrigeminal cistern and that lipoma can also bloom on GRE is necessary. Additional fat sat (FS) sequences as T1FS and T2FS or computed tomography (CT) are be required for the confirmation of the lipoma as demonstrated in our case. Here we also discuss the imaging characteristics of intracranial lipomas specifically blooming on GRE sequence.
| Case Reports|| |
We report the case of a rare lipoma in the quadrigeminal cistern in a 18-year-old female presenting with headache. She was referred to our hospital by a local physician. Neurological and systemic examinations were normal. Blood analysis was within normal limits and EEG did not show abnormal discharges.
Cranial magnetic resonance (MR) demonstrated a small well-defined rounded area of altered signal-intensity, abutting the dorsum of the tectal plate, in left para-sagittal region in the quadrigeminal cistern (peri-mesencephalic) cistern. It showed marked hyperintensity on T1-weighted (T1-W) images and hypointense on T2-weighted (T2-W) images [Figure 1]a and b. A signal drop out was seen on the GRE images [Figure 1]c. No restriction was seen on diffusion weighted images (DWI). These signal intensities were consistent with fat. Sagittal MR revealed a normal corpus callosum.
|Figure 1: 18-year-old girl presenting with headache. (a) Sagittal T1- weighted and axial T1-weighted magnetic resonance imaging (MRI) scan (done on Siemens MAGNETOM Avanto 1.5 Tesla MRI Machine)) in a 18-year-old female demonstrating a small hyperintense lesion (yellow arrow) in left quadrigeminal cistern (*) abutting the dorsum of the tectal plate (ƒ¢). Normal corpus callosum (white arrow). (b) T2- weighted MRI image demonstrating hypointense lesion (yellow arrow) in left quadrigeminal cistern (*). (c) Gradient echo image demonstrating a "signal drop out" (yellow arrow) in the left quadrigeminal cistern. (d) Noncontrast axial computed tomography (CT) image demonstrating the same lesion in the left quadrigeminal cistern as a hypodensity (yellow arrow) having fat attenuation (CT value: −50−60 HU)|
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The same lesion on CT appeared as a sharply demarcated homogeneous low density lesion (CT value: −50 to −60 HU) indicative of a lipoma [Figure 1]d.
Another similar case of lipoma in quadrigeminal cistern in a 6-year-old male presenting with three episodes of episode of febrile convulsions associated with postictal drowsiness for 25-30 min since last 6 months.
Normal birth and developmental history. Neurological and systemic examinations were normal. Blood analysis was within normal limits and EEG was suggestive of epileptiform activity in bilateral temporal lobes.
Cranial MR demonstrated a small well-defined rounded area of altered signal-intensity abutting the inferior colliculus, in the the right para-sagittal region in quadrigeminal cistern. It showed marked hyperintensity on T1-weighted (T1-W) images and hypointense on T2-weighted (T2-W) images [Figure 2]a and b. A signal drop out was seen on the GRE images [Figure 2]c. No restriction was seen on DWI images. These signal intensities were consistent with fat. Sagittal MR revealed a normal corpus callosum.
|Figure 2: A 6-year-old male three episodes of episode of febrile convulsions. (a) Sagittal T1-weighted and axial T1-weighted magnetic resonance imaging (MRI) images (done on 1.5T Siemens machine) showing a well-defi ned hyperintensity (red arrow) in right para-median region of quadrigeminal cistern (*). It is abutting the inferior colliculus (black arrow). Corpus callosum is normal (white arrow). (b) T2-weighted MRI image showing well defi ned hypointensity (red arrow) in the right|
quadrigeminal plate cistern. (c) Gradient echo image showing a "signal drop out" (red arrow) in the right quadrigeminal plate cistern
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| Discussion|| |
Intracranial lipomas are very rare and constitute <0.1% of intracranial tumors.  Intracranial lipomas are neither hamartomas nor true neoplasms; rather, they are congenital malformations.  Half of intracranial lipomas are associated with midline brain malformations of varying severity which include hypoplasia/aplasia of corpus callosum and vascular abnormalities. 
Intracranial lipomas result from abnormal persistence and mal-differentiation of meninx primitiva (considered to be the origin of the dura, arachnoid and pia mater).  Most frequent location of intracranial lipomas is in the quadrigeminal region of the brain. Commonly being asymptomatic, are detected incidentally. 
The exact etiology of intracranial lipomas is still a matter of discussion. Earlier, theories regarding the histogenesis were illustrated which include:
- Hypertrophy from preexisting fatty tissue of the meninges,
- Metaplastic meningeal connective tissue,
- Heterotopic malformation of dermal origin, and
- Tumor-like malformation derived from primitive meninx. 
Another theory was hypothesized that lipoma being midline structured are mainly due to improper neural tube closer defects. Case reports have been published illustrating associations of lipoma with other midline defects such as spina bifida and meningomyeloceles.  At present, intracranial lipomas are accepted to be due to the abnormal differentiation of the persistent meninx primitive. It is this region that constitutes the inner level of the pia, arachnoid, and dura. 
A retrospective pediatric study with 20 patients found that 50% of the intracranial lipomas were interhemispheric and 25% were found at the quadrigeminal cistern.  A quadrigeminal region lipoma has previously been reported as lipoma in the quadrigeminal cistern, the quadrigeminal plate, the ambient cistern, the superior vermis, or the superior medullary velum.  Corpus callosum, quadrigeminal/superior cerebellar cistern, suprasellar/interpeduncular cistern, cerebellopontine angle cistern and sylvian cistern are the common sites. Only 20% of patients with lipomas of the quadrigeminal plate/ambient cistern are symptomatic. 
We reported two patients with incidental lipoma of the quadrigeminal region. These lesions are benign and need no further treatment.  It is important to be aware of the occurrence of the lipoma in the quadrigeminal plate cistern and that they do bloom on GRE. Blooming on GRE could raise the suspicion of subarachnoid haemorrhage. Subarachnoid haemorrhage requires prompt and expert management as against lipoma which is just an incidental finding. The cause of blooming of lipomas on GRE is not established in literature. Small accretions of calcium in the capsule as well as within the lipomas are reported on histopathology literature.  Hence calcium was thought to be the cause of blooming on GRE and susceptibility-weighted imaging. Microscopic calcifications are visible only on susceptibility weighted images due to chemical shift artifact. If the chemical environment is significantly different between adjacent structures, a shift in the precessional frequency of nuclei can occur.  The chemical shift phenomenon is most noticeable at lipid and water interface, which are exaggerated on GRE sequences. The approximate chemical shift between the lipid and water is 3.5 ppm which translates to 224 Hz separation at 1.5 T field strength.  The chemical misregistration is a result of the inability of the system to identify the frequency displacement caused by chemical shift and special frequency encoding. This misregistration causes dark or bright band at interfaces. Findings in our series suggest the chemical shift artifact is the likely cause of blooming.
Other T1 intracranial hypterintense lesions which could be seen in this region are dermoids, teratoma and thrombosed vascular structures.
Dermoid cysts are rare, benign, congenital ectodermal inclusion cysts that account for approximately 0.3% of all intracranial tumors. , Most common location of intracranial dermoid cysts is at the midline in the sellar and parasellar compartments, fourth ventricle, and vermis.  Location of dermoid in the quadrigeminal cistern is relatively uncommon. On CT these lesions tend to be well-defined, nonenhancing soft tissue/cystic masses with fat attenuation as that of lipomas. On MRI, dermoid cysts typically show high signal-intensity on T1-weighted images, variable signal-intensity on T2-weighted images, and lack of enhancement on contrast-enhanced images.  These signal characteristics are nearly same as those of a lipoma. Dermoid tumors demonstrate heterogeneous attenuation values which could help in differentiating these from lipoma.
Intracranial teratomas are most commonly found in the cerebral hemispheres and pineal gland. At MRI, they typically manifest as multiloculated cystic/solid mature components lesions that contain calcifications and fat, which are responsible for their high-signal-intensity appearance on T1-weighted images. However its rarity for occurrence in the basal cisterns and absence of cystic/solid component in our case helped in excluding teratomas in our cases. 
Thrombosed vascular structures as veins can also appear bright on T1-WI and T2-WI suggesting loss of flow void and bloom on GRE as in lipoma. However draining a thrombosed vessel is always is always seen to have supplying arterial feeder and a venous drainage. These were absent in our case and hence diagnosis of thrombosed vascular channel was excluded.
Rarely a direct surgical approach is required for the treatment of intracranial lipomas. Surgery is indicated only when these tumors grow in size, sufficient to cause a mass effect or intracranial hypertension. When strongly adherent to important vessels, despite of using microsurgical techniques, the preservation is very difficult. ,
Also, surgical management may result in high morbidity and mortality due to high vascularity of intracranial lipomas and their strict adhesion with adjacent tissue. 
Surgical management should be considered only in those epileptic patients who fail to respond to the medical treatment and in which a relation between tumour location and symptoms has been recognised. 
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. Also surgery would be unnecessary for stable or asymptomatic cases if the lesion does not grow or compress brain tissue. 
| Conclusion|| |
Any midline or para-median lesion in the quadrigeminal cistern (peri-mesencephalic cistern) with signal-intensity which has signal characteristics of fat on MRI or CT should be considered to be an intracranial lipoma. However, the possibility of intracranial dermoid with high fat content can be considered only if the lesion has a heterogeneous appearance.
Knowledge of occurrence of quadrigeminal cistern lipoma is necessary. Many intracranial lipomas show blooming on GRE, which could be confused for haemorrhage. However CT and additional FS sequence would help to come to a final diagnosis. Intracranial dermoid is another entity with fat signal and should also be considered if the lesion has heterogenous appearance on MRI.
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[Figure 1], [Figure 2]