2012, Lieberson, Epidermoid Cysts.

Journal of Radiosurgery and SBRT Vol. 0 2011 1

Case Report

CyberKnife radiosurgery can control recurrent epidermoid cysts of the central nervous system

Robert E. Lieberson, MD,1 Amanda Mener,1 Clara Choi, MD PhD,1 Maziyar A. Kalani, MD,1 Scott G. Soltys, MD,2 Iris C. Gibbs, MD,2 Gary Heit MD PhD,3 John R. Adler, MD,1 and Steven D. Chang, MD,1

1Department of Neurosurgery, Stanford University Medical Center, Stanford, CA, USA2Department of Radiation Oncology, Stanford University Medical Center, Stanford, CA, USA3Department of Neurosurgery, Kaiser Permanente Group, Redwood City, CA, USA

Corresponding Author: Robert E. Lieberson, MD, Department of Neurosurgery, Stanford University, 300 Pasteur Drive, Room R-205, Stanford, CA 94305, USA, [email protected], +1-650-723-5573 (office), +1-650-725-1784 (fax)

(Received August 3, 2011; accepted August 26, 2011)

Epidermoid cysts of the central nervous system may be difficult to resect and recurrent lesions may be impossible to control with open surgery. We identified three patients with recurrent epidermoids treated with radiosurgery at Stanford. One patient with a middle fossa lesion that had been resected twice in six years, presented with a 4.5 cubic centimeter recurrence and was treated with radiosurgery. Follow-up scans over three years showed no additional growth. Two patients had spinal lesions. One had undergone numerous, unsuccessful procedures in the three years before the radiosurgical treatment and subsequent open resection of a 3.8 cubic centimeter recurrence. His scans remain unremarkable eight years after treatment. The other, with acaudaequina mass, had required five open resections in 11 years. Following the last resection, the residual was treated radiosurgically. The lesion eventually increased in size,but became symptomatic only after seven years. A second course of radiosurgery was delivered. We believe that stereotactic radiosurgery can be safe for some epidermoid cysts of the central nervous system, decreases their growth rate, and may facilitate subsequent open surgery. It should be considered for select individuals with recurrent or unresectable lesions.

Key words: Epidermoid Cyst, Central Nervous System, Brain, Spine, Stereotactic Radiosurgery, CyberKnife, Gamma Knife, Linear Accelerator

INTRODUCTION

Epidermoid cysts of the central nervous system (CNS) are rare, accounting for only 0.3% to 1.8% of intracranial mass lesions [1] and 0.7% those in the

spine.[2] They originate from embryonal cell rests left behind during embryogenesis or following trauma. [3, 4] Epidermoids may be difficult to resect completely and are prone to recurrence. [5, 6]

Conventional radiotherapy treatment has been reported for intracranial [7] and spinal epidermoids. [8]Kida et al [9] first described the use of stereotacticra-diosurgery (SRS) for intracranial epidermoids. We are unaware of any other reports discussing the use of SRS for spinal epidermoids.

We present one recurrent intracranial epidermoid and two recurrent spinal epidermoids treated with CyberKnife SRS.

METHODS

With the approval of the Institutional Review Board, we identified and reviewed the records of three patients with recurrent epidermoids treated at the Stanford CyberKnife Center. Members of the Neurosurgery Department reviewed their diagnostic imaging studies and re-examined each of the patients.

CASE REPORTS

Patient 1

In September 1999, patient 1, a 53 year-old woman, presented to our spine clinic with a two-month history of

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R. E. Lieberson et al.

2 Journal of Radiosurgery and SBRT Vol. 0 2011

progressively severe, intermittent, bilateral lower extremity numbness, weakness and cramping without bowel or blad-der complaints. The examination showed only 4/5 weak-ness in the left tibialis anterior and extensor hallucislongus. A magnetic resonance image (MRI) scan demonstrated an intramedullary lesion of the conus, 3.9 centimeters (cm) in greatest extent. In October 1999, patient 1 underwent a T

12 to L

2 laminectomy, gross total resection of the epi-

dermoid. Within a year, her symptoms returned. In Octo-ber 2000, we performed a second open resection a for a 3.8 cm recurrence seen on MRI. The surgeon reported that it was impossible to develop a plane between the cyst wall and the cord and a gross total resection could not be completed. Painful recurrences in July and August of 2001, which were both associated with increased numb-ness, worsened weakness, and incontinence of bowel and bladder. Two MRI-guided-aspirations of prominent cystic components were completed, removing 4 cubic centim-eters (cc) and then 2 cc of keratinized material from the lesion, reducing its volume by approximately 30% by MRI. An MRI in May 2002 (Figure 1A) showed a 3.8 cm recurrence and, consequently, the patient received SRS. In a single session, we delivered a marginal dose of 18 Gray (Gy) to the 81% isodose line. The patient’s pain, numbness, weakness, and incontinence improved within weeks. Three months following SRS, an additional aspiration procedure was required. Because of recurrent symptoms, in January 2003, the lesion was re-explored and the 2.3 × 1.4 × 1.2 cm recurrence was removed with intraoperative monitoring. During surgery, there was a well-developed cleft around the lesion and it was possible

to easily separate and remove at least 80% of the cyst wall from the cord. Only the most cranial and caudal compo-nents could not be resected due to changes in monitor-ing potentials with manipulation of those portions. At her most recent neurosurgical follow-up visit in June 2009, she was clinically stable, complaining only of residual bladder incontinence and hypalgesia of the right foot. Although two small areas of cyst wall were not removed, the most recent, post-operative MRI showed no evidence of any residual (Figure 1B).

Patient 2

Patient 2, a 62-year-old man at the time, was first seen at Stanford in February 2004. He had undergone-four separate L

3 to S

1 laminectomies for pain, numb-

ness, and weakness (1991, 1995, 1999, and 2002). MRI scans in 2003 showed a residual lesion extending from L

3 to S

1. In February 2004, the fifth was completed. At

surgery, it was felt that the entire contents of the cyst and most of the cyst wall had been removed. Because of his history of multiple prior recurrences, elective SRS to the resection cavity followed the open procedure. A total of 22Gy prescribed to the 81% isodose line was delivered in two sessions to the 39.6 cc resection bed. Symptoms of pain, a unilateral foot drop, and numbness remained stable. In January 2011, increasing urinary symptoms led to an MRI, which showed a cystic recur-rence, with a cavity measuring 7.1 cm in greatest extent. We felt that an open surgery would unlikely be effec-tive and recommended an additional course of SRS. In March 2011 we delivered 22Gy prescribed to the 75% isodose line in two sessions (Figure 2). In the brief time

Figure 1. Patient 1. The image on the left (A), shows a T2 weighted MRI obtained prior to radiosurgery in 2002. A 3.8 cm cystic recurrence is seen within the conusmedullaris at the L1-2 level.The image on the right (B), shows a similar T2 weighted MRI taken following both radiosurgery and the open resection. There is no evidence of residual tumor within the conus.

Figure 2. Patient 2. This image shows the most recent radiosurgical plan as delivered in 2011. The black outline surrounds the cystic, epidermoid lesion. The white outline surrounds the nerve roots, anterior and to the right of the mass.


Radiosurgery for recurrent epidermoids (revised)


that has elapsed following treatment, there have been no changes in complaints or findings.

Patient 3

Patient 3, a 48-year-old man, was referred to Stan-ford in November 2007. The patient related a his-tory of headaches and seizures which began in the early 1990s. Computerized tomography (CT) scans at that time were reportedly unremarkable. By 2000, increasingly symptoms prompted a re-evaluation, and an MRI showed a 3.7 cm diameter lesion occupying right anterior middle fossa. Aftera first craniotomy and reported gross total resection in October 2000, an MRI showed no residual. Serial MRI scans showed a recurrence that by July 2006, was 3 cm in greatest diameter. A second right temporal craniotomy was completed and it was felt that a gross total resection had been achieved. Although the immediate post-op-erative scans reportedly showed no residual, only one year later, a follow-up MRI showed a 2.3 cm diam-eter recurrence in the sylvian fissure and suprasellar cistern. He was referred to Stanford for SRS. At the time, the patient reported increased headache and five to six seizures per day, but the physical examination was unremarkable. In November 2007, we delivered a marginal dose of 24Gy prescribed to the 75% isodose line, in three sessions, for a lesion measuring 2.3 cm in maximum diameter and 4.5 cc in volume (Figure 3A). The most recent scan of August 2010 showed that the lesion remained unchanged by MRI (Figure 3B). When last examined, in November 2010, the patient was seizure free and denied significant headaches.

DISCUSSION

Epidermoid cysts are also known as cholesteoto-mas or “pearly tumors.” Verattus is credited with the first description of an epidermoid in 1745 and in 1807, Pinson, an artist working with Dupuytren at the Hotel Dieu, constructed a wax model of one of these lesions.[10] Cruveilhier, a French pathologist, characterized them more completely in 1829 and described them as having a “mother-of-pearl” appearance. [11] In 1839, Mueller coined the term “cholesteotoma” because of the abundant choldesterol crystals seen in some specimens and, since then, any masses containing cholesterin have been referred with this moniker. Von Remakfirst identi-fied their epithelial cell origin in 1854. [12] It was not until 1920 that the first successful surgical treatment of an epidural was described by Bailey. [13]

Epidermoids of the CNS originate from embryo-nal cell rests or from fragments of epithelial tissue left behind following surgery, lumbar puncture, or other trauma. [3, 4] They are composed of squamous epithe-lial cells and connective tissues components surround-ing degenerated, desquamated skin. Epidermoids do not contain skin appendages, such as hair. [14] They grow slowly along natural cleavage planes, and may be clinically apparent only after years of growth. [5] Malignant transformation is uncommon. [15] They are more common in women (54%) and, although most are congenital, they often do not present until the fifth decade. [14] Headache, seizures, intracranial hyperten-sion, and focal deficits related to lesion location are the most common presenting symptoms and signs. Epider-moids are usually homogeneously hypodense on CT, and may have an enhancing rim or irregular calcified inclusions. On magnetic resonance imaging (MRI), they are hypointense on T1-weighted sequences and hyperintense on T2-weighted images. [5] The differ-ential diagnosis may include arachnoid cysts and less commonly glioma, metastasis, lymphoma, or infection, and MRI diffusion studies may be helpful in differenti-ating epidermoids from other cystic lesions of the CNS.[3, 16, 17] Epidermoids occur in the cerebellopontine angle (37.3%), theparasellar cisterns (30%), the middle cranial fossa (18%), within the diploë (16%), or in the spinal canal (5%). [18-20] Although most epidermoids are in the intradural-extramedullary space, they can be extradural, or transdural, and they will rarely occur within the substance of the spinal cord and intramedul-lary epidermoids of the brain have been reported. [3, 6, 21] Epidermoids exhibit linear, rather than logarithmic growth, explaining their slower expansion compared to some CNS tumors. [22] Surgical gross total resection remains the goal for most treatment, but there remains controversy regarding the appropriateness of subtotal

Figure 3. Patient 3. The image on the left (A), shows the most recent radiosurgical plan, completed in 2007.The image on the right (B), is the most recent MRI, obtained following the radiosurgicaltreatmentof 2010. There has been no interval change or increase in the size of the lesion.




resection when the risk of post-operative deficits might be increased. [5]

Although radiotherapy has been described as inef-fective for epidermoid cysts, [3, 5, 11] its successful use has been described. [7, 8] Parikh et al reported that 50Gy delivered in 25 daily sessions yielded radiographic and symptomatic control of a previously resected, recurrent cerebello-pontine angle epidermoid after a two-year period of follow-up. [7] Bretz et al treated a recurrent intraspinal C6-T2 epidermoid, causing sensory and motor deficits, with 46 Gray in 23 daily fractions. [8] The patient, followed radiographically for two years and clinically for six years, remained stable without increased symptoms or evidence of re-growth.

Kida et al [9] first reported the use of stereotactic radiosurgery (SRS) for intracranial epidermoids. They treated seven patients with trigeminal neuralgia or hemi-facial spasm secondary to posterior fossa cysts. The pain or spasms resolved in five of their seven patients after Gamma Knife therapy. They achieved local control in all of their patients, and in two patients, the lesions reportedly decreased in size after a mean follow-up of 52.7 months. We were unable to find any other reports describing the use of radiosurgery for intracranial epi-dermoid cysts. We are aware of no prior reports describ-ing the use of SRS for spinal epidermoids.

In our three patients, SRS was safe, we saw no radiation related complications, and SRS appeared to prevent or delay recurrence. Patient 3, who had a mid-dle fossa lesion, had radiographic recurrences within a year following each of two craniotomies. MRI scans show him to be disease free three years after radio-surgery. Patient 2 had required five open resections in a period of 13 years; an average of one operation every 2 ½ years. Following the last open surgery, we delivered SRS to the resection cavity and patient 2 did not require any additional intervention for seven years. Patient 1 had undergone two open and two percutaneous proce-dures in the 2 ½ years before SRS. Although ongoing symptoms forced us to re-resect the epidermoid shortly after the SRS treatment, patient 1 now remains without radiographic or clinical evidence of a recurrence after eight years. We believe that, without SRS, the time to the next recurrence for each of our patients would have been similar to that observed before SRS. Although we are confident that we delayed the recurrence of the lesion, we cannot assume that we have achieved any cures. Epidermoids are slow growing and the time to recurrence can be a decade or more. [22]

We have used SRS in a variety of situations. For patient 3, SRS was used to treat a recurrence following surgery. Repeat courses of radiosurgery for recurrences have previously been reported as safe for a variety of other conditions, including arteriovenous malforma-tions, [23] acoustic neuromas, [24] ependymomas,

[25] chordomas, [26] and nasopharyngeal carcinomas.[27] Radiosurgery to the resection bed of a metastasis improves local control. [28] Patient 2 received SRS both to treat a post-operative resection cavity and also as a salvage procedure for a recurrence after SRS. SRS has been employed to decrease vascularity prior to planned resections for hemangioblastomas, [29] renal cell metastases, [30] and arteriovenous malformations.[31] SRS may create an improved capsule or a more defined plane around some lesions. Kamitani et al, reported that a capsule around the radiated hemangiob-lastoma, “made resection easy.” [29] Sanchez-Mejia et al reported that following SRS, the tissue planes of separation around the AVMs were more “distinct.” [31] Patient 1 was treated with SRS prior to an unplanned open resection. At surgery, we found a clear plane that separated most of the lesion from surrounding cord, facilitating a near total resection.

Patient 1’s care was particularly interesting for two reasons. First, we believe that the lesion was more eas-ily resected as a result of the SRS treatment. Patient 1 had undergone four procedures before the SRS treat-ment. During each operation, the intramedullary conus lesion could not be separated from the surrounding cord. Shortly following SRS, and because of increasing symptoms, we were forced to operate. Whereas before SRS we were unable to develop a plane around the lesion before SRS, after SRS it was possible to remove the lesion almost entirely because of a well developed cleft that had not been present at the time of the earlier oper-ations. Second, patient 1’s unplanned surgery following SRS might have been predicted. Since the expansion of the cavity in other cystic lesions, such as hemangiob-lastomas, does not stop for some time after SRS, we believe that this may also be true for epidermoids.

Patients with multiply recurrent epidermoids have a high-risk of complication. Given the location of the lesions in our patients, had additional open surger-ies been required, there would probably have been injury to the involved structures of the cavernous sinus (patient 3) or to the conus and caudaequina (patient 2 and patient 1). Others have argued that a gross total resection is not always the best approach and, alternatively, a debulk-ing with planned subsequent surgeries over the course of a patient’s lifetime may be safer. [3, 5, 32, 33] Instead, consideration of planned post-operative radiosurgery for those patients where a gross total resection is not possible, or is excessively risky, might be appropriate.

Although we have not seen evidence of any radia-tion related complications in our patient population, potential risks could include radiation necrosis or mye-lopathy. Epidermoids can also spontaneously undergo malignant degeneration. [15] Although the mechanism is not well understood and is thought to involve chronic inflammation, cyst rupture, and subtotal resection of the


Radiosurgery for recurrent epidermoids (revised)


cyst wall, [34] SRS could theoretically increase the risk of a malignant conversion.

CONCLUSION

Others have discussed radiation therapy and SRS as possible treatments for epidermoids of the central nervous system, however, we describe the first use of SRS for spinal epidermoid cysts. Our patients all had multiply recurrent lesions and we believe that the use of SRSprevented or significantly delayed subsequent recurrences. We believe that SRS should be considered for some epidermoids that are difficult or impossible to resect, or for epidermoids in patients who would not tolerate or might not accept an open procedure. For those patients who must have surgery because of mass effect, but for whom a gross total resection might be excessively risky, a planned subtotal resec-tion followed by radiosurgery might be an appropriate consideration. Our recommendations are preliminary. The study of a larger cohort, followed for a much longer period, would be required to perfect treatment recommendations.

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