Epidermoid Cyst On Brain Stem Case Study

Intracranial tumours may rarely present with stroke, which is mostly related to invasion, compression, or encasement of intracranial vessels by the tumour mass.1–3 Intracranial epidermoid tumours often develop in the cerebello-pontine angle where they cause symptoms and signs of a slowly expanding mass lesion.4 Although epidermoid tumours are known to produce a mass effect and occasionally to narrow intracranial vessels, it is very unusual for them to present with sudden ischaemic symptoms.5 Reduced blood flow from mechanical stretching of the pontine arteries by intra-arachnoidal expansion of the tumour may be one possible cause of a stroke.

We report two cases of cerebello-pontine angle epidermoid tumours presenting with signs of brain stem stroke. This phenomenon has not been reported before.

CASE REPORTS

Case 1

This 45 year old man presented with a sudden attack of slurred speech, nausea, vertigo, and impaired coordination of the right hand, which resolved partially within three hours. His personal history was unremarkable. On neurological examination, in addition to dysarthria he had a left hemiparesis and hemihypoaesthesia. Magnetic resonance imaging (MRI) of the brain showed right sided cerebello-pontine angle and cerebellar peduncle lesions, which were hypo- and hyperintense on T1 and T2 weighted images, respectively. On diffusion weighted (DW) MRI, both lesions were hyperintense, which suggested that they were a cerebello-pontine angle epidermoid tumour and a cerebellar peduncle infarct (fig 1). Routine laboratory tests and echocardiography were normal. Following a course of medical treatment for two weeks, the patient underwent a right suboccipital retrosigmoid craniotomy, which showed a classical pearly tumour encasing and stretching the branches of the basilar artery and anterior inferior cerebellar artery. The tumour was totally removed and the patient did well after surgery.

Figure 1

 (A,B) Axial T2 weighted magnetic resonance imaging (MRI) of case 1 showing stretching of the basilar artery (arrow) and its branches (arrows) by the tumour. (C) A hyperintense right mid-pontine lesion consistent with infarction (arrow) and right cerebello-pontine angle epidermoid tumour (double tip arrow). (D) Diffusion weighted MRI showing an infarct (arrow) in the right upper pontine level, and stretching of the basilar artery and its branches (double tip arrow) by the cerebello-pontine angle epidermoid tumour.

Case 2

This 39 year old woman presented with sudden neurological deficits including vertigo, nausea, and numbness on the right side of her face and the left side of her body. Her personal history was otherwise normal. On neurological examination she reported hypoaesthesia in dermatomes 2 and 3 of the fifth cranial nerve and she had a left hemiparesis with a positive Babinski sign. Cranial MRI showed left cerebello-pontine angle and left cerebellar peduncle lesions that were hypo- and hyperintense on T1 and T2 weighted images, respectively. Both the lesions showed high signal intensity on DW images, again suggesting a left cerebello-pontine angle epidermoid tumour and a left cerebellar peduncle infarct (fig 2). Following a course of medical treatment the patient underwent a left sided suboccipital retrosigmoid craniotomy, which revealed tumour related stretching of the perforating branches of the basilar artery. The tumour was removed except for a piece of capsule which was adherent to the pons. The postoperative course was uneventful without additional deficits.

Figure 2

 (A, B) Axial T2 weighted and CISS magnetic resonance imaging (MRI) of case 2 showing stretching of the vertebrobasilar artery (arrows) and its pontine perforating branches (arrow). (C) Axial T2 weighted MRI of case 2 documenting the left cerebello-pontine angle epidermoid tumour (double tip arrow) and brain stem infarct (arrow) at the mid-pontine level. (D) Diffusion weighted MRI showing the cerebello-pontine angle epidermoid tumour with prominent high signal intensity and infarction at the mid-pontine level (arrow).

DISCUSSION

Cerebello-pontine angle epidermoid tumours may present with symptoms of cranial nerve, cerebellar, and brain stem compression as well as with obstructive hydrocephalus and meningeal irritation.6–8 They tend to spread along the cerebello-pontine angle/prepontine cisterns and compress or encase but not invade the adjacent structures. A sudden neurological deficit as a presenting symptom, however, is a very exceptional event which has been reported only once for a parasellar dermoid cyst.9 Meningiomas are known to cause stenosis or occlusion of intracranial vessels, and recently cases of vessel wall invasion by glial tumours have been also reported.1,3 However to the best of our knowledge, this type of presentation has never been described for epidermoid tumours.

Epidermoid tumours have a thin capsule consisted of stratified keratinised squamous epithelium which may rupture spontaneously causing bouts of chemical meningitis. Although the resulting inflammatory reaction has been suggested as a cause of capsular adherence to brain stem, there is no evidence that this type of inflammation induces a vasculitic response of the brain stem vessels. Our patients did not report any previous complaints suggesting a bout of chemical meningitis. Epidermoid tumours have been reported to cause facial palsy by impairing blood supply (as well as causing other cranial neuralgias by direct compression), by pushing the cranial nerve against a blood vessel, or by local irritation from cholesterol spillage.10 Presentation with sudden ischaemic symptoms is extremely unusual11–13 and our review of published reports did not reveal any such case of an epidermoid tumour that caused brain stem infarction as a presenting symptom. Diffusion weighted MRI of the brain is very useful not only in differentiating among epidermoid tumours, cerebello-pontine angle arachnoid cysts, and infarction, but also in evaluating postoperative follow up of residual tumour and recurrences.14,15

Although it is generally believed that the clinical course of epidermoid tumours is benign, awareness of presentation with brain stem ischaemia is important. In these two cases both patients were relatively young, non-smokers, and otherwise healthy individuals. We conclude that tumour induced stretching of the branches of the basilar artery, especially of the anterior inferior cerebellar artery, led to stroke. Preoperative imaging studies as well as intraoperative findings further supported this assumption.

REFERENCES

Abstract

Epidermoid cysts involving the brainstem are extremely rare, with only 18 reported cases in the literature and only five purely intrinsic epidermoid cysts within this group. “White epidermoids”, a rare entity, have high protein content and show reversed signal intensity on magnetic resonance images. In contrast to the classical variety, these cysts show high signal intensity on T1-weighted images and low signal intensity on T2-weighted images. Here, we report an interesting case of intrinsic brainstem “white epidermoid cyst” in a 15-year-old girl and discuss its clinical characteristics, radiological features, and surgical treatment. The girl presented with a one-year history of progressive quadriparesis, and features of multiple cranial nerve involvement. Because the cyst was purely intrinsic and had altered signal intensity, the diagnosis was initially unclear until definitive neuroimaging was performed using diffusion-weighted magnetic resonance imaging (DW-MRI) sequences.

Keywords: Brainstem, epidermoid cysts, intrinsic, white

Introduction

Epidermoid cysts are rare, slow-growing, congenital, space-occupying lesions accounting for 0.2-1.8% of all primary brain tumors.[1] Epidermoid cysts involving the brainstem are extremely rare, with only 18 reported cases in the literature and only five purely intrinsic epidermoid cysts within this group.[2] Typically, epidermoids appear hypointense on T1-weighted magnetic resonance (MR) images, and hyperintense on T2-weighted sequences. Rare “dense” or “white epidermoids” have high protein content and show reversed signal intensity on MR images, with high signal intensity on T1-weighted images and low signal intensity on T2-weighted images.[1] Here, we report an interesting case of intrinsic brainstem “dense” or “white epidermoid cyst” in a 15-year-old girl. The clinical presentation, radiological imaging, and surgical management are discussed, along with a review of pertinent literature.

Case Report

A 15-year-old girl presented with a one-year history of progressive quadriparesis, diplopia, dysphagia, dysarthria, and unsteadiness of gait with frequent falls to either side. Her neurological examination revealed upper motor neuron type of quadriparesis with multiple cranial nerve involvement (V, VI, IX, X, and XII). There were no clinical or laboratory signs of infection. Brain MR imaging (MRI) demonstrated an atypical intra-axial pontomedullary lesion, which had a high T1 signal, a low T2 signal, and subtle contrast enhancement [Figure 1]. Initial working diagnoses included intrinsic brainstem astrocytoma and cavernoma. For further confirmation, a diffusion-weighted imaging (DWI) sequence was obtained [Figure 2], which revealed a bright signal within the tumor suggestive of an epidermoid cyst rather than a cavernous malformation or brain tumor. The patient underwent a midline suboccipital craniotomy. On splitting the vermis, the floor of the fourth ventricle was exposed and found to be distended from the underlying cyst. A myelotomy was performed through the thinned-out floor, revealing a pearly white, viscous substance that was resected gross totally with the aid of micro-neurosurgery. Postoperatively, the patient experienced mild, transient sixth cranial nerve palsy that resolved completely within several weeks. Postoperative computed tomography (CT) scan confirmed the intraoperative impression of gross-total removal [Figure 3], and histological testing confirmed the presence of an epidermoid cyst.

Figure 1

Sagittal T1-weighted brain magnetic resonance imaging showing an apparently intra-axial space-occupying lesion of the pontomedullary region (a) with subtle contrast enhancement (b), the lesion is hyperintense in axial T1-weighted images (c) and hypointense...

Figure 2

Magnetic resonance diffusion-weighted image revealing a bright signal within the tumor

Figure 3

Postoperative computed tomography scans sagittal (a) and axial (b) demonstrate gross-total removal of the brainstem tumor

Discussion

Epidermoid cysts are rare, slow-growing, congenital, space-occupying lesions accounting for 0.2-1.8% of all primary brain tumors.[1] These primarily arise in the basal subarachnoid spaces and commonly involve the cerebellopontine angle and juxtasellar areas.[3,4,5,6] Those located in the brainstem occur very rarely, and purely intrinsic lesions as described in the present case have been reported previously in five cases only.[2]

Epidermoid cysts develop slowly, and the onset of neurological symptoms is usually gradual. Patients harboring these cysts typically become symptomatic between the ages of 20 and 40 years.[6,7] Due to the insidious manner in which these grow, brainstem epidermoid cysts in children are extremely rare and have been reported in eight cases only.[7] The pathogenesis of true intra-axial brainstem epidermoid is unclear and usually not considered in the preoperative differential diagnosis of brainstem tumors. Although considered as histologically benign, epidermoid cysts can cause significant neurological defects by compressing vital structures.[4] Patients presenting with intrinsic epidermoid cysts commonly exhibit symptoms related to the compression of associated brainstem structures. In the present case, the presentation suggested lesion enlargement that resulted in pyramidal tract involvement, multiple cranial nerve palsy, and balance problem.

The best diagnostic clue is a cerebrospinal fluid (CSF)-like mass that insinuates within cisterns, encasing adjacent neurovascular structures.[2] Typically, epidermoids appear hypointense on T1-weighted MRI scans, but might also have an intermediate intensity between the brain and CSF on T1, whereas they are usually hyperintense on T2-weighted sequences.[7,8] However, signal intensity can be variable depending on the relative amount of lipid, cholesterol, keratin, and proteins and seldom show contrast enhancement.[8] Rare “white epidermoids” have high protein content and may appear hyperattenuated on CT scans. Compared with the classic epidermoid cyst, these “dense” or white epidermoids show reversed signal intensity on MR images, with high signal intensity on T1-weighted images and low signal intensity on T2-weighted images.[1] The rarity of brainstem epidermoid cysts can make their diagnosis difficult; thus, the use of modern MRI techniques, such as DWI and fluid attenuated inversion recovery (FLAIR) imaging, might be helpful in establishing the diagnosis in such cases.[7] They do not suppress completely on FLAIR images and restrict (show high signal intensity) on DWIs. In our case, the radiological presentation was unusual, fitting rightly to the rare type of “white epidermoids”.

Although there appears to be a consensus about surgical resection being the best therapeutic option for the treatment of epidermoid cysts, these tumors pose a surgical challenge and attempts for aggressive removal of the cyst wall are fraught with increased risks of morbidity and mortality. On the other hand, cases treated more conservatively show good or excellent results with minimal complications. Nevertheless, Ziyal et al.[8] pointed out that surgical resection should be as radical as possible. Neurosurgical judgment at the time of surgery is warranted to ensure maximum resection while minimizing postoperative neurologic deficits.

Conclusion

Childhood onset purely intrinsic white epidermoid cyst involving the brainstem is very rare. The use of modern diffusion-weighted MRI techniques might be helpful in establishing the diagnosis in such cases. Neurosurgical judgment at the time of surgery is warranted to ensure maximum resection while minimizing postoperative neurologic deficits.

Footnotes

Source of Support: Nil

Conflict of Interest: None declared.

References

1. Katzman GL. Diagnostic Imaging: Brain. Salt Lake City, Utah: Amirsys; 2004. Epidermoid cyst; p. I-7-16.

2. Recinos PF, Roonprapunt C, Jallo GI. Intrinsic brainstem epidermoid cyst. Case report and review of the literature. J Neurosurg. 2006;104(Suppl 4):285–9.[PubMed]

3. Berger MS, Wilson CB. Epidermoid cysts of the posterior fossa. J Neurosurg. 1985;62:214–9.[PubMed]

4. Cobbs CS, Pitts LH, Wilson CB. Epidermoid and dermoid cysts of the posterior fossa. Clin Neurosurg. 1997;44:511–28.[PubMed]

5. Toglia JU, Netsky MG, Alexander E., Jr Epithelial (epidermoid) tumors of the cranium. Their common nature and pathogenesis. J Neurosurg. 1965;23:384–93.[PubMed]

6. Ulrich J. Intracranial epidermoids. A study on their distribution and spread. J Neurosurg. 1964;21:1051–8.[PubMed]

7. Caldarelli M, Colosimo C, Di Rocco C. Intra-axial dermoid/epidermoid tumors of the brainstem in children. Surg Neurol. 2001;56:97–105.[PubMed]

8. Ziyal IM, Bilginer B, Bozkurt G, Cataltepe O, Tezel GG, Akalan N. Epidermoid cyst of the brain stem symptomatic in childhood. Childs Nerv Syst. 2005;21:1025–9.[PubMed]

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