Giant cell tumors involving the spine are rare. In a literature review by Shankman et al. [1], only 2.7% of the 1,277 giant cell tumors reported were located in the spine. Sanjay et al. [2] reported that from 1955 to 1990 there were only 24 patients with giant cell tumors of the spine at the Mayo Clinic. The tumor usually develops in the vertebral body, and the posterior elements are frequently involved in patients with advanced lesions.

Although the features of giant cell tumors of the appendicular skeleton have been well described in the literature, there are few reports of MRI of vertebral tumors, which are limited to case reports and a few examples included in general reviews of spinal lesions [1–3]. In this study, the clinical records and MRI findings of 10 patients with giant cell tumors of the spine were reviewed retrospectively to define the typical MRI features of these unusual lesions.

Giant cell tumors of bone in the vertebrae are quite rare. Most of these lesions occur in the sacrum, followed in order of decreasing frequency by the thoracic, cervical, and lumbar segments [3]. Spinal lesions are more frequently found in women and affect patients in their second to fourth decades of life [4]. The clinical symptoms are primarily pain (often with a radicular distribution), weakness, and sensory deficits. A dramatic increase in lesion size can occasionally be associated with pregnancy and is presumably related to hormonal stimulation [3]. However, in our series, only one case was detected in the cervical spine. More men were affected than women (M:F = 7:3).

Pathologically, giant cell tumor consists of abundant osteoclastic giant cells intermixed throughout the spindle cell stroma. Mononuclear cells in a giant cell tumor are of more significance than the giant cells [5]. The other features of this lesion include occasional erythrocyte lakes (secondary “aneurysmal bone cystlike” change) and xanthomatous changes within the focal collections of histiocytes. Aneurysmal bone cyst formation may be encountered as a secondary feature in a variety of osseous lesions including giant cell tumor [6]. In addition, prominent areas of fibrous tissue with a high collagen level are a frequent finding, and giant cells are uncommon in these regions.

The presence of a single marrow lesion in the axial skeleton on MR images poses a diagnostic problem of primary bone tumor or metastasis. Although a biopsy of the lesion remains the mainstay of an ultimate diagnosis, the imaging characteristics of a lesion might be helpful in directing the most appropriate further investigations.

Radiologic studies of spinal giant cell tumors usually show an expansile lesion, with osteolysis observed on radiographs [7]. As with appendicular giant cell tumors, spinal lesions show no evidence of mineralized matrix [4]. In the sacrum, the lesions are frequently large with destruction of the sacral foraminal lines, but this nonspecific finding is also observed with other large sacral lytic lesions. A sacral giant cell tumor commonly involves both sides of the midline, and an extension across the sacroiliac joint is frequent [8]. In this study, invasions to the sacroiliac joint were also detected in two cases of the three sacral masses. Paradoxically, giant cell tumors of the long bones do not share this invasive feature of spinal lesions and rarely extend across or through the articular cartilage. When a giant cell tumor occurs in the spine above the sacrum, it usually affects the vertebral body as opposed to the posterior elements and is accompanied by many other neoplasms (aneurysmal bone cyst, osteoid osteoma, or osteoblastoma). Extension into the posterior elements and paraspinal soft tissues and associated vertebral collapse are often apparent [7].

The MR images of a giant cell tumor often show heterogeneous signal intensity regardless of the pulse sequence used [9]. Generally, the tumor has low to intermediate signal intensity on the T1-weighted MR images. Interestingly, giant cell tumors have low to similar signal intensity to the normal spinal cord on the T2-weighted MR images in 63–96% of cases [9]. This appears to be caused by the relative collagen content of fibrous components and hemosiderin within the tumor [6]. When bone tumors do not contain a mineralized matrix, the low signal intensity areas observed on MR images are not always the result of hemosiderin deposition and can be caused by a dense collagen matrix [6].

Although this feature is not unique to giant cell tumors of the spine, it is quite helpful in making a differential diagnosis because most other spinal neoplasms (metastases, myeloma, lymphoma, and chordoma) show high signal intensity on the long-TR MR images. This appearance may be the initial imaging characteristic suggestive of a correct diagnosis. Evidence of hemorrhage may also be apparent with high signal intensity on the T1- and T2-weighted images or fluid–fluid levels on the MR images. Cystic areas (similar to those seen in aneurysmal bone cyst) and regions of previous hemorrhage with hemosiderin deposits are common [4]. In this study, cystic changes were also noted in four cases, and a fluid–fluid level was observed in one case. MRI performed after an IV injection of contrast material also shows enhancement of the lesion, which reflects its increased vascular supply.

In the present case series, nine patients showed the unusual appearance of low signal curvilinear areas on the T1- and T2-weighted images within the vertebral body, which presumably corresponds to a multicystic lesion with a thickened trabeculae, fibrous septae, or hemosiderin deposit. The curvilinear area of low signal intensity was described previously for plasmacytoma and vertebral hemangioma [10]. A solitary bone plasmacytoma needs to be considered in a differential diagnosis. However, heterogeneous signal intensity on the T2-weighted images, heterogeneous enhancement, and cystic changes were not usually observed in vertebral hemangioma.

Disease control after a complete surgical excision for a giant cell tumor is 85–90% successful in the tubular bones. However, giant cell tumors in the axial skeleton, particularly in the sacrum, are associated with a poorer prognosis because the tumors are larger and more difficult to excise completely [11]. In many cases, a complete resection is only possible in limited sacral lesions, and imaging plays a key role in a presurgical evaluation. In general, sacral lesions that spare the majority of the S1 segment and the sacroiliac joint are amenable to a complete excision. Giant cell tumors that cannot be excised entirely are often treated with a combination of partial curettage and radiation therapy [12]. The estimated frequency of malignant giant cell tumors or a malignant transformation of benign giant cell tumors is 10% [12]. In most cases, the malignant transformation develops after irradiation. Radiation therapy, though controversial due to the potential risk of causing the sarcomatous degeneration of benign tumors, may provide a reasonable method for controlling the tumors in these cases [12].

In conclusion, the MRI findings of a giant cell tumor in the spine are often characteristic, allowing for an accurate diagnosis and preoperative evaluation of the extent of the mass. The characteristic findings include an expansile mass with heterogeneous low to intermediate signal intensity on the T2-weighted image, curvilinear area of low signal intensity on the T1- and T2-weighted images, and cystic changes within the mass.

Address correspondence to H. W. Chung ([email protected]).