A giant cell tumor of the cranial base treated by stereotactic radiosurgery

Abstract

Giant cell tumors (GCTs) developing from the cranial bones are rare. Occurrence of these tumors in the vicinity of eloquent areas precludes complete excision. Fractionated external beam radiotherapy (FEBRT) has been used for those cases, but with inconsistent outcomes. The authors report a case of a patient with a GCT involving the left occiput which was successfully treated by CyberKnife stereotactic radiosurgery (CK RS). There was improvement in the neurological deficit and occipital pain without adjunctive treatment. This is the first report of stereotactic radiosurgery (SRS) adopted as a primary treatment modality for a cranial GCT.

1. INTRODUCTION

Giant cell tumors (GCT) comprise 3-7% of primary bone neoplasms.¹ The cranial bones, which develop via intramembranous ossification are rare sites for giant cell tumors which actually develop by endochondral ossification.² Giant cell tumors of the skull are frequently locally-invasive in a manner similar to GCTs of the extremities. The cranial lesions may give rise to neurological abnormalities, which depend upon the region involved. Giant cell tumors which occur in the vicinity of eloquent areas preclude a complete excision. We report on a case in which stereotactic radiosurgery (SRS) was used as the sole treatment in a patient who was diagnosed with a GCT involving the left cranial base.

2. CASE REPORT

2.1 History and Examination

This 39-year old woman presented to our Emergency Room (ER) with severe left occipital pain which occurred when she extended her neck. She had a 6-month history of left tongue atrophy and limited tongue movement. She had undergone a brain computerized tomographic scan (CT) and brain magnetic resonance imaging (MRI) at an outside hospital 2 months prior to our ER admission. The studies documented a bone mass involving the left skull base. The lesion was biopsied at the time of the imaging studies at the same outside hospital: the histopathology was that of a GCT. She had not undergone any treatment since the diagnostic biopsy.

Examination at the time of this ER visit revealed bilateral cervical muscle spasms and limitation of neck motion by 30 degrees during flexion and by 20 degrees during extension. Left tongue atrophy and limitation of tongue motion suggestive of a left hypoglossal nerve dysfunction was also demonstrated. The occiput to C4 spine CT at presentation showed an expansile and lytic bone lesion involving the left skull base including the medial and caudal temporal bone, clivus, and the left occipital bone without brain parenchymal involvement (Fig.1). She was offered various treatment options including surgery, external beam radiotherapy (EBRT) and SRS. Considering the close proximity of the lesion to the brainstem and left occipital condyle, SRS was recommended by the neurosurgeon as the optimal treatment modality and the patient concurred with this plan.

Figure 1.

CT axial bone window image (left) and coronal reconstructive image (right) demonstrating a destructive mass of the left occipital condyle.

2.2 Radiosurgery

At the time of the SRS set-up, the patient’s head position was secured with an Aquaplast Mask and a 1.25-mm slice thickness planning CT was carried out. Imaging data from the CT was then imported to the treatment planning station and reconstructed using Multi-Plan fusion software (Accuray Inc., Sunnyvale, Calif., USA).

The treatment plan was then formulated: the target dimensions were 3.7 x 3.5 x 1.7 cm and the treatment volume was 17.396 cc. The treatment plan consisted of a dose of 18 Gy to the 77% isodose line using a 15-mm collimator. The maximum dose to the tumor was 23.37 Gy and the peripheral dose to the tumor margin was 16.6 Gy at the 77% isodose line. The modified conformality index was 1.04. The brainstem dose was kept to less than 30% of the prescription dose (Fig.2). The outpatient treatment with CK RS (Accuray Inc., Sunnyvale, Calif., USA) consisted of two fractions of 9 Gy given on a daily basis for 2 days.

Figure 2.

Axial (upper left), sagittal (upper right), and coronal (lower left) isodose distributions and dose volume histogram (DVH) (lower right) in the target and adjacent tissue.

2.3 Postradiosurgery Follow-Up

Follow-up imaging studies were performed initially at three months after the radiosurgery treatment, then every six months for next two years, followed by once each year for next two years, and every two years at present. The follow-up period was nine years. During the post-treatment period, the tumor size remained stable on follow-up MRIs (Fig.3). On neurological examination one year after radiosurgery, the patient’s occipital pain, disturbed tongue motion, and limitation of range of neck motion had all improved. She hadn’t experienced any adverse effects from the radiosurgery treatment.

Figure 3.

Axial Gd-enhanced T1-weighted image (left) and coronal T1-weighted image (right) demonstrates a stable mass of the left occipital condyle without mass effect 9 years after SRS.

3. DISCUSSION

Giant cell tumor of the bone usually manifests with benign histologic features, but can be locally aggressive and rarely can metastasize. Twenty percent of GCTs are malignant. Benign GCT has a 3:2 female predilection and usually manifests in the third and fourth decades of life.³ The mainstay of the treatment of GCTs of the bone is complete surgical excision. After total resection, local control is achieved in 85-90% of all cases.³ Incomplete resection, however, is frequently associated with tumor recurrence in up to 50% of such cases.⁴

Despite improvements in surgical techniques, complete tumor removal without causing functional deficits remains challenging in some regions, especially in the skull base or spine.⁴ When GCT involves a location where complete resection is not possible, EBRT or SRS can be used.

Much investigation has been carried out to determine an effective treatment plan for the radiotherapeutic control of GCTs, including dosage and fractionation. With regard to the EBRT literature, Feigenberg et al.⁵ found a local control rate of 77% in a series of 26 lesions treated with EBRT using doses of 35 to 55 Gy with standard daily fractions ranging from 1.67 to 2.33 Gy per day (median, 1.80 Gy per day). Schwartz et al.⁶ observed a local control rate of 85% using doses of 42 to 68 Gy in 23-34 fractions. Seider et al.⁷ presented a result of 70% tumor control using doses of 36-66 Gy in the maximum 30 fractions.

Modern imaging techniques, including computerized 3-dimensional imaging reconstruction and CT-assisted treatment planning has resulted in an increased conformality and thus improved accuracy with safety to adjacent normal tissues. Roeder et al.⁸ reported five patients with GCTs treated with intensity-modulated-radiotherapy (IMRT) to a median dose of 64 Gy in conventional fractionation (single dose 1.8-2 Gy, five fractions per week), which resulted in a local control rate of 80%. Because of the scarcity of skull base GCTs, a generally accepted dose or fractionation concept for various types of radiosurgery is lacking.

At this time, SRS such as CK RS allows a high-dose of radiation to be delivered to tumors with an optimal dose conformity. Therefore, this technique offers the possibility of high tumor control rates without major side effects.⁹

Our patient had a locally-invasive large tumor, which developed in the left occipital bone with compression of the medulla and left cerebellum. She had neck motion-dependent pain suggestive of instability of the craniocervical junction and left hypoglossal nerve dysfunction. After the SRS, the symptoms and neurological deficits have been improving. Over a nine-year follow-up, the series of imaging studies have not shown any brain parenchymal abnormality. Based on this experience, we feel that SRS could be the primary treatment modality for invasive and unresectable GCTs.

4. CONCLUSIONS

This study reports a case of GCT which occurred in the base of the skull and which was solely treated by SRS for the first time in the medical literature. During the long follow-up period, the tumor remained stable and the patient had no adverse effects related to radiation. This case suggests that SRS can be a viable primary treatment option for giant cell tumor of the skull base.