Introduction

Epidermoids are rare, benign, slow-growing lesions that arise from retained ectodermal remnants. They account for 0.2–1.8 % of all intracranial tumors and up to 7 % of cerebellopontine angle (CPA) tumors [23, 24, 29]. Lesions characteristically spread along anatomical cleavage planes, progressively filling the subarachnoidal spaces.

Despite being histologically benign, epidermal cysts pose a neurosurgical challenge, mainly in case of recurrent tumors. Surgical removal is the treatment of choice, which should aim for an extensive resection with preservation of the patient’s neurological function [29].

Radical surgery is not always achievable and carries significant risk of perioperative complications including cranial nerve deficits, hydrocephalus, and aseptic meningitis, due to the release of epidermoid breakdown products [2]. Because of the high surgical morbidity, balance between extent of resection and a patient’s functional preservation might be taken into consideration, especially in multioperated patients, harboring recurrent lesions with intra-axial extension.

The authors describe an innovative technique for cisternal shunting of recurrent, cystic, unresectable brainstem epidermoids.

Study design

The authors describe the case of a recurrent cystic brainstem (BS) epidermoid tumor. A literature review has been performed on PubMed and Google Scholar, using the search terms “brainstem, epidermoid, cerebellopontine angle, cyst, and recurrent”.

A total of 24 papers reporting the management of BS epidermoid tumors resulted from the electronic search. Papers report both pediatric and adult cases. Table 1 summarizes data obtained from the literature review.

Table 1 Review of the literature
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Case report

A 5-year-old female was referred to our institution in January 2001 with cognitive impairment, dysphagia, and gait disturbances.

The neurological examination at hospital admission revealed left hemiparesis and a complete right VI cranial nerve palsy. A contrast-enhanced MRI showed a voluminous cystic lesion of the prepontine cistern extending into the pons.

A right retrosigmoid approach was performed; because of brainstem invasion, tumor capsule could not be completely peeled off. Histological examination was diagnostic for epidermoid tumor. Postoperative course was uneventful, with a complete recovery of the hemiparesis and of the VI cranial nerve palsy.

In September of 2002, a contrast-enhanced MRI pointed out a small intraparenchymal cystic tumor recurrence at the medullary-pontine junction (Fig. 1a, b); since the patient was asymptomatic, a wait-and-see approach was undertaken.

Fig. 1
figure 1

MRI study showing tumor recurrence on axial (a) and sagittal (b) T2-weighted images; postoperative MRI study showing the presence of the cystic-cisternal shunt (yellow arrow), with complete relief of tumor bulk-related mass effect on axial (c) and sagittal (d) T2-weighted images; MRI study, performed at last FU, showing the persistence of the cyst-cisternal shunt (yellow arrow) without disease progression on axial (e) and sagittal (f) T2-weighted images

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In January of 2003, the patient started complaining of worsening headaches, with a MRI showing a volumetric increase of the intraparenchymal cystic component, which split brainstem white matter fibers, causing severe mass effect.

The patient underwent right retrosigmoid approach with magnum foramen decompression. Cisternal arachnoid adherences were resected through microdissection technique, freeing neurovascular structures from scaring adhesions in order to restore cerebrospinal fluid circulation.

The intraparenchymal lesion component was opened through smooth dissection and the lining tissue gross-totally removed, taking care to avoid spillage of cyst contents into the subarachnoid space. Perioperative administration of corticosteroid and intraoperative irrigation with hydrocortisone was adopted to minimize the risk of chemical meningitis. Once the cyst was completely emptied, useless attempts to peel tumor capsule, tightly attached to the brainstem, were avoided.

Residual cyst was shunted into the cisternal space using a small catheter, which was left in place at the opening site of the brainstem lesion. The catheter was modeled in a J-shaped fashion using a 3-0 silk stitch, which helped to maintain the shunt system in place and to direct drainage flow according to spinal fluid circulation (Fig. 2).

Fig. 2
figure 2

The intraoperative placing of the cyst-cisternal shunt: overview of the CPA after the placing of the shunting system (a); particular of the catheter at higher magnification (b). BS brainstem, C catheter, D dura, Ep epidermoid, LCN lower cranial nerve, V fifth cranial nerve, VIII eighth cranial nerve

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The postoperative course was uneventful (Fig. 1c, d). The patient was followed up for 142 months after the shunting operation. At the last clinical evaluation, the neurological exam was within the norm without radiological evidence of recurrence (Fig. 1e, f).

Discussion

Internal shunting of intracranial cysts has already been described in rare instances, for example in case of cystic craniopharyngiomas or arachnoidal cysts, to release tumor-related compression to the surrounding tissue, as an alternative therapeutic option in patients not eligible for surgical resection [3, 7].

To the best of our knowledge, only 24 cases of brainstem epidermoid tumors have been previously reported, both in the pediatric and adult population, with disappointing results in terms extent of surgical resection, recurrence rate, and post-operative morbidity (Table I) [1, 4–6, 8, 10–22, 25–28, 30, 31]. The present case represents the one with the longest follow-up ever published in the literature.

As widely known, since epidermoids are not sensitive for radiation/chemotherapy, making surgery the treatment of choice for these lesions. Over the last decades, the spread of endoscopy and the advancements made in neurosurgical techniques have dramatically improved the results of CPA epidermoid surgery. Nevertheless, resection of these tumors still requires high technical skills, mainly because of their invasive growth pattern, which put tumor bulk in tight relationships to critical neurovascular structures.

A crucial point in a surgeon’s decision-making is weather to stop or proceed with the peeling of the tumor capsule from neurovascular structures. Being non-neoplastic, slow-growing lesions, loss of function in order to achieve complete tumor removal is not justifiable. This means that the surgeon should take care to prevent any morbidity and should not attempt to remove the portion of tumor capsule tightly attached to neuro-vascular structures [24, 29]. For this reason, compared to overall data referred to extent of resection of intracranial epidermoids, CPA lesions carry a relatively lower gross-total resection rate, which account for less than 75 % of cases [23].

Subtotal resection can lead to progressive production of keratin, resulting in cyst recurrence and risk of chemical meningitis [24, 29]. Notably, it occurs in less than 40 % of patients undergoing subtotal resection and it is directly related to the amount of residual cyst [9, 23]. Nevertheless, perioperative administration of corticosteroid and intraoperative irrigation of the surgical site with hydrocortisone has been proven to be effective in minimizing that risk. Moreover, the use of steroids is reported to reduce the risk of postoperative communicating hydrocephalus, which may develop after an intense period of meningitis or following leakage of the cyst contents [23, 29].

Besides the complication following subtotal removal, the main factors, which have to be considered, in terms of extent of surgical resection, are the patient’s age, adhesion of the capsule to surrounding neurovascular structures, number of previous surgeries, and the patient’s preoperative neurological status. Surgery of recurrent intra-axial lesions should aim to relieve brainstem compression due to tumor mass effect. In these patients, balance between extent of resection and functional preservation might lead to subtotal removal, carrying a low risk of long-term recurrence. Even in case of subtotal resection, indeed, the overall estimated recurrence rate of these tumors is 24 % of cases [2].

The authors described an innovative surgical technique for the shunting of recurrent, cystic, unresectable epidermoids into the subarachnoid space through a J-shaped ventricular catheter. The described procedure avoids dangerous attempts to peel the tumor capsule, often not distinguishable from the brainstem parenchyma. The catheter is modeled in order to stay in place indefinitely, acting as a shunt system for the cyst contents clearance.

Conclusions

Cyst-cisternal shunting in case of recurrent, intra-axial brainstem epidermoids appears to be a safe and long-term effective technique to relieve mass effect and brainstem compression.