Introduction

While many spinal lesions designated as Giant Cell Tumours (GCT) in the past probably were aneurysmal bone cysts and other lesions which may exhibit prominent multinucleated giant cells [1, 11], it is now evident that whereas GCT constitutes about 5 per cent of all bone tumours, GCT originating in the spine are rare and comprise less than 0.5 per cent of all tumours arising in the vertebral column.

The sacrum is much more frequently the site of origin of GCT than the other spine levels [6, 7, 13] and GCT arising in the thoracic spine is extremely rare [18]. There is an ongoing debate as to the biological classification of GCT and of all bone neoplasms, its behaviour in individual cases is the most difficult to predict. It has a high local recurrence rate, with tumour recurring at the site of origin in as many as 50 per cent of cases [3, 4, 8, 9], but GCT has rare metastatic potential [2].

Opinions regarding the malignant potential of GCT have ranged between the belief that most if not all conventional GCT are low-grade malignant or “semimalignant” [20] tumours; that metastasizing GCT are true malignant GCT which have evolved or transformed from conventional GCT [10]; that malignant GCT is a separate tumour from conventional GCT [16]; or, that most so-called malignant GCT are other mis-diagnosed bone sarcomas with areas of pseudo-GCT differentiation [10, 16].

The management of GCT is plagued by the high recurrence rate following curettage alone and the considerable risk of sarcomatous transformation in tumours treated by irradiation [3, 5, 17, 19].

Depending upon the accessibility of the tumour, the incidence of recurrence may be substantially reduced by a combination of curettage and repeated liquid nitrogen instillation [14, 15]. However, there is some evidence that GCT in the spine have a more favourable prognosis than those arising in the appendicular skeleton [6].

Against this background of possible misdiagnosis, high local recurrence rate following curettage, propensity for malignant transformation following irradiation, unpredictable metastatic potential and the great rarity of GCT arising in the thoracic spine, we described the management of a patient who presented with an intrathoracic mass considered initially to be lung cancer but which was unexpectedly and uniquely diagnosed as GCT by the microscopic finding of multinucleated giant cells in a pleural effusion.

The extensive surgical procedure needed to extirpate the tumour, which had infiltrated the mediastinum and chest wall and restore stability to the spine following destruction of the T5 and T6 vertebrae is outlined.

Case report

Presenting features

A 34-year-old man presented to his general practitioner with a history of mild back pain in the mid-thoracic region on the right side, which was worsened by lying in the left lateral position. He had no past and present cardiac or respiratory symptoms.

Radiography, CT, and MRI

Chest X-ray (Fig. 1) revealed a large mass within the mid-thoracic cavity where it showed well-circumscribed distinction from the adjoining lung but merged indistinctly with mediastinal structures at about the T4–T6 level. A pleural effusion was present on the right side.

Fig. 1
figure 1

At initial presentation the postero-anterior chest radiograph showed a large mass in the right thorax having a well-defined interface with the lung but indistinct involvement within the mediastinum

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At this initial assessment stage the differential diagnosis included a primary neoplasm of the lung, an unusual manifestation of tuberculosis or other infectious lesion, or tumour arising from within the mediastinum.

CT scanning (Fig. 2) confirmed the well-circumscribed border between the mass and the adjoining lung tissue and the presence of a thin bony shell defining the lateral border of the mass.

Fig. 2
figure 2

The axial CT at T6 shows the distinct boundary and shell of bone (arrow) between the tumour and the lung and revealed the destruction of the vertebral body and right pedicle of T6 with encroachment into the spinal canal

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Medially the mass had extensively replaced bone of the T5 and T6 vertebrae and posteriorly it appeared firmly attached to the chest wall. MRI scans confirmed the presence of tumour within the T5 and T6 vertebra with preservation of the T5-6 disc and a relatively uniform signal throughout the mass, which was enhanced by gadolinium (Fig. 3).

Fig. 3
figure 3

The T2-weighted MRI shows substantial homogeneity throughout the tumour and the lack of the destruction of the T5-6 intervertebral disc despite the extensive destruction of the T5 and T6 vertebral bodies above and below

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A bone scan confirmed that no other skeletal lesions were present and myelography did not add to the information already gained from CT and MRI. Angiography confirmed that while the major vessels had been displaced by the tumour there was no extension into the vessel walls.

Cytology and biopsy histopathology

The pleural effusion was aspirated and cytological examination of the fluid revealed large multinucleated giant cells having numerous nuclei (Fig. 4a). Needle biopsy of the chest mass carried out under CT control showed the presence of conventional benign GCT differentiation (Fig. 4b).

Fig. 4
figure 4

a Photomicrograph of a multinucleated giant cell which was present in large numbers in the pleural effusion. Giemsa ×500. b Photomicrograph of tissue sample from the intrathoracic mass showing a benign Giant Cell Tumour of bone composed of prominent multinucleated giant cells scattered within a stroma of mononuclear cells and many vascular channels. Haematoxylin–eosin ×200

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Surgery

While the patient consented to undergo surgical resection and spinal reconstruction, he specifically refused permission for embolization to be carried out during the surgical procedure if the need arose.

Surgery commenced with a posterior exposure from T3 to T8 to allow access to the posterior parts of T5 and T6 involved by tumour and sufficient to enable instrumentation of the spine by inserting anchoring devices (DePuy-ISOLA/Raynham, MA, USA) into T3, T4, T7 and T8.

A decompressive laminectomy at the T5 and T6 levels confirmed the presence of spinal cord compression by the tumour, which was thoroughly curetted prior to final assembly of the stabilizing devices and wound closure.

The patient was next placed in the left lateral decubitus position. A myofascial rotation flap was prepared from latissimus dorsi in readiness for reconstruction of the chest wall before entering the chest through the sixth intercostal. The right fifth and sixth ribs were retained for reconstruction of the anterior weight-bearing column. The tumour was adherent to the upper and middle lobes of the right lung and was interposed between the azygos vein and segmental vessels.

The T5 and T6 nerve roots were encased within tumour. Excision of the tumour included removal of the right upper lobe and part of the middle lobe of the right lung; the right T5 and T6 nerve roots; and, the azygos vein and accompanying segmental vessels. Following removal of these structures and the main tumour mass multiple biopsies of the exposed bed were taken to assess clearance. The anterior weight-bearing column was then reconstructed using the retained ribs as strut grafts and the chest wall was closed by incorporating the latissimus dorsi flap fashioned for that purpose.

The surgery lasted 16 h during which the patient lost 11 L of blood. The patient had refused permission for embolization to be used if needed and there is little doubt that the blood loss would have been substantially diminished by embolization of the extensive vasculature within and around the tumour bed.

Pathology

Microscopic examination of the tumour showed the characteristic features of a conventional GCT with large numbers of osteoclast-like giant cells and a stromal cell component comprising spindle-shaped mononuclear cells. The tumour was richly vascular and showed extensive zones of haemorrhage. While there were occasional giant cells within vascular channels, commonly seen in benign GCT, there was no necrosis, cellular atypia or other feature suggestive of malignancy. There was an extensive shell of new bone demarcating the periphery of the intra-thoracic portion of the tumour but no evidence of bone or cartilage differentiation within the main tumour mass. Between the outer margin of the tumour and the adjoining adherent lung there was a narrow zone showing fibrin undergoing organization to form collagenized scar tissue. Following the surgical resection no tumour was identified in the multiple biopsies taken from the tumour bed.

Post-operative course

The patient made a satisfactory recovery and was able to ambulate independently within a month of surgery. Post-operative chest X-rays showed expansile residual right lung and the anterior vertebral column construction became firmly incorporated with the spine balanced in the sagittal plane.

Five years after surgery the patient is in good health and there are no signs of recurrence of the tumour.

Discussion

This case provides a valuable reminder of the ability of GCT to destroy existing bone, to permeate soft tissue structures such as mediastinal compornents, and to grow to a large size at first presentation with minimal symptoms. While very rarely arising in the thoracic spine where its proximity to important mediastinal and other soft tissue structures can pose particular problems for surgical extirpation as seen in our patient, surgery alone is the treatment of choice nevertheless, as the risk of malignant transformation is substantial following irradiation of GCT. With an extensive tumour, as in our patient, the surgical procedures utilized need to take into account the fact that GCTs are prone to recur following curettage and the facility of GCT to be implanted into soft tissues also has to be taken into account.

A seemingly novel feature of our patient was the unexpected finding of multinucleated giant cells in a pleural effusion , which allowed GCT to be entertained as an initial diagnosis prior to its subsequent confirmation by needle biopsy and later extensive histopathology of the surgically resected tumour. The finding of giant cells in the pleural fluid indicates that an invasive GCT may shed component tumour cells into serous cavities in a fashion similar to the situation when cancer cells are found in the pleural fluid when malignant lung tumours extend to involve the visceral pleura. However, there was no evidence of seeding of the pleural surfaces by GCT in our patient and it is interesting to speculate as to whether this would have occurred at a later stage, especially since GCT is recognized as a tumour, which can readily undergo implantation in soft tissues by implantation along needle biopsy tracks and in tissue incisions [12].

Finally, the fact that our patient has a stable spine and is symptom-free 5 years after surgery shows that technically difficult radical excision can be rewarded by successful cure even when a GCT is extensive and involves key anatomical structures.

Conclusion

We reported an extreme rare case of a very large conventional GCT of bone arising in the thoracic spine and extending widely through the mediastinum to protrude as a large mass within the right pleural cavity, which contained a small pleural effusion. The initial favoured diagnosis of lung cancer or mediastinal neoplasm was corrected following the unexpected finding of multinucleated giant cells in the pleural effusion and characteristic histology in a needle biopsy.