A rare case of white pearls in brainstem.

Intrinsic brainstem epidermoid is extremely rare, and only 14 cases have been reported. Authors report a classic case of brainstem epidermoid in a 14-year-old male child presenting with symptoms of brainstem involvement. The child underwent a successful surgical excision. The lesion was intrinsic and caused diagnostic dilemma based on conventional radiological images. Based on our experience in this case and a thorough review of literature, we are of the opinion that diffusion-weighted images are very important in establishing the diagnosis. Such lesions are challenging and attempt to remove adherent tumor capsule may produce additional neurological deficits.

Introduction

Epidermoid cysts account for 1–2% of all intracranial tumors.[123] Epidermoid tumors were first described by French pathologist Cruveilhier as the most beautiful of all tumors, and he termed them “tumeur perlee.”[456] The common site of intracranial occurrence is the cerebellopontine angle, parasellar region, lateral, and fourth ventricle. Intra-axial brainstem epidermoid cysts are extremely rare, and only a few cases have been reported in world literature.[1234] Authors report a case of symptomatic pediatric brainstem epidermoid and describe radiological differential diagnosis, surgical management, and pertinent literature review.

Case Report

A 14-year-old previously healthy male patient presented to our outpatient clinic with a 4 months history of headache, dysphagia, nasal regurgitation of fluids, hoarseness of voice, and gait ataxia. On neurological examination, he had bilateral horizontal gaze nystagmus, lower cranial nerve (IX, X, and XII) involvement, and left upper motor neuron type palsy.

Magnetic resonance imaging brain [Figure 1] revealed a solid cystic lesion measuring 2.9 cm × 2.7 cm × 2.4 cm involving medulla and lower pons, which was not enhancing on contrast [Figure 2]. Lesion showed a restriction on diffusion-weighted (DW) sequences. A radiological diagnosis of brainstem epidermoid was established.

Figure 1

Magnetic resonance imaging brain (axial, coronal, and sagittal) showing intrinsic brainstem lesion which is hypointense on T1-weighted images (a-c) and hyperintense on T2 (d-f) suggestive of intrinsic brainstem glioma

Figure 2

Axial contrast magnetic resonance imaging (a) showing no contrast enhancement. Axial diffusion-weighted image (b) show classical restriction suggestive of intrinsic brainstem epidermoid. Axial susceptibility weighted imaging (c) and postoperative noncontrast computed tomography head (d)

After detailed evaluation, the patient was taken for definitive surgery. A midline suboccipital craniotomy with resection of tumor was performed in the prone position. Tumor bulge was noticed at pontomedullary junction, and cranial nerves V, VII, and IX were displaced posterolaterally. Myelotomy was performed at the level of sulcus limitans on the thinned floor to enter the tumor. Tumor consisted of typical pearly white thick cheesy, flaky, viscous substance suggestive of epidermoid. A near total excision of this intrinsic tumor could be performed using standard microneurosurgical techniques, and only the adherent part of the capsule was left behind [Figure 3]. The postoperative course was uneventful, and the patient did not develop any fresh neurological deficit.

Figure 3

Intraoperative images showing the floor of the fourth ventricle (a), intrinsic brainstem lesion exposed by performing myelotomy (b and c). Classical cheesy, flaky lesion can be seen confirming intraoperative diagnosis of epidermoid (d)

Histopathology of tumor tissue further revealed keratin pearls and confirmed the diagnosis of brainstem epidermoid cyst [Figure 4].

Figure 4

Histopathology of tumor tissue revealed keratin flakes, consistent with contents of an epidermoid cyst

Discussion

Epidermoid cysts account for about 1% of all intracranial lesions and usually affect middle age group. Pediatric epidermoid cysts are rare. The brainstem is the extremely rare site for epidermoid, and till date, only 14 pediatric cases have been reported[789] [Table 1].

Table 1

Literature review of pediatric brainstem epidermoid

The embryonic basis of epidermoid cyst is traced to 3–5 weeks with a displacement of epithelial remnants at the time of neural tube closure. Usually, the lateral sites are preferred for epidermoid as cell remnants move with otic vesicles or neurovascular complex.[101112]

Epidermoid is composed of outer capsule, inner epithelial layer, and cystic fluid. The outer connective tissue layer surrounds the inner stratified squamous epithelium.[91013] Epidermoid is a slow growing benign tumor and increase in size is due to the breakdown products of desquamated cells which accumulate to form cholesterol-rich deposit and flaky, cheesy material. The growth of epidermoid is similar to that of epidermal cells, and they have the propensity to spread along the open cisternal spaces.[1511]

Brainstem epidermoid cysts grow slowly and can lead to multiple symptoms, ranging from cranial nerve palsies, obstructive hydrocephalus, and long tract signs.

The cysts exhibit a higher signal intensity then cerebrospinal fluid on T1, T2 weighted images and cause classical restriction on DW images (DWIs).[7811] The signal intensity varies depending on the protein, lipid, cholesterol, and keratin content.[6910] Sometimes, the radiological picture is misleading and other differentials such as arachnoid cyst, cholesterol granuloma, glioma, and dermoid may be considered.[891213] Without DWIs, these lesions can be mistaken for glioma, but one differentiating feature from intra-axial brainstem glioma is a lack of edema.

DWIs play a crucial role in differentiating epidermoid from abscess, glioma, and arachnoid cyst. In the current case, all radiological findings were compatible with the diagnosis of intrinsic brainstem epidermoid.

The main modality of treatment of brainstem epidermoid is surgical excision.[13691113] Care should be taken to avoid spillage of cyst contents as it may lead to postoperative aseptic meningitis. It is recommended to provide perioperative steroid cover.[3] Complete excision may not be feasible in some cases due to adherence of cyst capsule to the critical neurovascular structure. Subtotal excision may be performed in such cases to prevent disastrous complications; however, there remains a risk of recurrence. Of the 14 reported cases of pediatric brainstem epidermoid, 5 died in postoperative period due to worsening of neurological status.[12345] Good long-term results may be obtained by a conservative approach in patients who are neurologically stable or were incidentally diagnosed. These patients require clinical and radiological follow-up. However, patients with profound deficits and those who present with worsening neurological symptoms need surgical excision.

Conclusion

Brainstem epidermoid should be considered a differential diagnosis in case of intrinsic brainstem lesions which show a restriction on DWI. In indicated patients, surgery is the treatment of choice. The goal of surgery is to achieve decompression, so as to decrease the mass effect. If the capsule is adherent to brainstem, then no attempt should be made to excise it.

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Conflicts of interest

There are no conflicts of interest.