Aggressive giant cell tumor of the anterior arc of the rib.

Giant cell tumor of bone also known as osteoclastoma is a distinct clinical, roentgenographic and pathologic entity with specific characteristics. It is a benign but locally aggressive neoplasm, classically seen as a purely lytic lesion of the epiphyseal or metaphyseal-epiphyseal region of long tubular bones extending to the articular surface. It usually occurs after skeletal maturation and is one of the rare bone tumors that more frequently affects women. Even though rarely it can occur in ribs, it usually occurs in the posterior aspect. We report here a case of giant cell tumor originating from the anterior arc of the rib diagnosed on fine needle aspiration cytology.

Introduction

Giant cell tumor (GCT) is a tumor found most often in the ends of long bones and is essentially located in the epiphyseal or metaphyseal or epiphyseal equivalent portions of bone. It is a locally aggressive neoplasm, generally arising in adults between the ages of 20 and 40 years, clinically possessing metastatic potential. It can also involve pelvic bones, vertebral bodies and small bones of digits. The rib is a rare site with a reported incidence of less than one percent. Even in the cases involving the rib, most were located in the posterior arc, i.e., the head and tubercle of ribs. Rare multicentric forms have been reported.[1-3] In this article, we report a case of GCT originating from the anterior arc of the rib which was diagnosed on fine needle aspiration cytology (FNAC).

Case Report

A 23-year-old female presented with a six-month history of a progressively growing mass in the right anterior chest wall associated with slight pain. The mass was hard, fixed to the chest wall and moderately tender. It measured 6 × 5 cm in its largest dimensions. The overlying skin was normal. She had no pulmonary symptoms. The acid phosphatase levels was 10.2 IU/L. All other hematological and biochemical investigations were within normal limits.

Patient underwent fine needle aspiration cytology. Cytological smears were cellular and comprising aggregates of uniform appearing spindled stromal cells and innumerable osteoclast type giant cells, having variable number of nuclei. The nuclei of the stromal cells resembled those observed in the osteoclast type giant cells. The stromal cells showed high nuclear to cytoplasmic ratio, with evenly distributed chromatin and inconspicuous to small nucleoli. No significant nuclear atypia was observed either in the giant cells or the background stromal cells. Mitotic figures were noted frequently [Figure 1]. In correlation with radiographic findings of an eccentric expanded lytic lesion with cortical erosion of anterior arc of fourth rib [Figure 2], a diagnosis of aggressive giant cell tumor of rib was offered cytologically. In our case, the musculoskeletal radiologist had opined an aneurysmal bone cyst and Askin tumor of anterior chest wall.

Figure 1

Aggregates of uniform appearing spindled stromal cells and innumerable osteoclast type giant cells (H and E, ×400). Inset showing histomorphology of the resected giant cell tumor (H and E, ×400)

Figure 2

Large expansile tumor mass with thinned out cortex in the anterior end of fourth rib noted on computed tomography scan

In view of the cytomorphological diagnosis and radiological cortical destruction of anterior arc of fourth rib, patient was referred to a surgical oncology centre with a possibility of soft tissue extension being also considered. At the higher centre, complete resection of the tumor was performed. The histopathological features suggested aggressive GCT of the anterior arc of rib. The cytomorphological features were in conjunction with that of histomorphological features observed.

Patient remained asymptomatic without evidence of recurrence at the end of one year following surgical intervention. At the last follow up her acid phosphatase levels had dropped to 6.1 IU/L.

Discussion

GCT of bone is an uncommon neoplasm accounting for about 4–5% of all primary bone tumors. The origin remains unknown. The giant cells may be derived from fused stromal cells of mononuclear phagocytic lineage. In fact, they may represent stromal precursor cells that have lost some of the detectable macrophage associated antigens or mononuclear phagocyte antigens seen in the more mature cells. GCT are generally considered benign but malignant cells can arise de novo or via transformation from a benign neoplastic giant cell lesion.[1-3]

Interestingly, GCT's are more common in females. Although the role of steroid metabolism in these lesions is unclear, estrogen and progesterone receptors have been identified in the cells of this lesion.[3]

The metaphyseal or epiphyseal zones of long bones are the most common sites, with 60% arising around the knee joint. Isolated cases have been reported in the scapula, sternum, patella, vertebra, skull and talus. Only few cases of GCT involving the ribs have been reported in the literature with most of them involving the posterior aspect. Due to its rarity, GCT arising from the chest wall is difficult to diagnose, especially when the tumor is located in the anterior arc of the ribs. It is also compounded by the fact that soft tissue counterpart of GCT is also known.[13-5]

Pain and an increase in local volume are the principal forms of presentation. Some patients present with pathological fracture resulting from weakening of the cortical bone. On a routine radiograph, GCT presents as an initially eccentric expanded lytic lesion, without a surrounding sclerotic halo, representing the cortical bone. As the lesion grows, it can encompass the entire circumference of the bone, causing rupture of the cortical bone, but a periosteal reaction is rarely seen.[1256]

Roentgenographic classification schemes have been used to characterize the tumor in any given case and attempt to predict the clinical outcome. Grading and staging of GCT have focused on (i). Histological features: Benign, aggressive and malignant, the latter having clearly pleomorphic features with abundant mitotic figures and (ii). Surgical staging: Clinically latent, active and aggressive.[3] In the present case, although there were no overt anaplastic features in the tumor cells, mitotic activity was frequently detectable. With the clinical symptomatic presentation of a rapidly growing mass and radiological evidence of bone destruction and expansion, a cytomorphological diagnosis of an aggressive GCT was offered in this case.

Giant cells are ubiquitous in bone lesions. A wide array of lesions may histologically mimic, depending on the quality and size of the biopsy. While examining lesions rich in these cells, if particular attention is paid to the background stromal cells and the clinico radiological data are correlated, then establishing the diagnosis becomes easier. A differential diagnosis of aneurysmal bone cyst (ABC), brown tumor, chondroblastoma, chondromyxoid fibroma (CMF), non-ossifying fibroma (NOF), giant cell rich osteosarcoma and malignant fibrous histiocytoma can be considered on cytology. In GCT, the giant cells are numerous in number and they are attached at the periphery of the clustered spindle cells. ABC can be primary or secondary to an underlying lesion like GCT or chondroblastoma. Aspirates from an ABC are generally hemorrhagic with sparse cellular yield comprised of scattered osteoclastic giant cells, spindle shaped fibroblastic cells and hemosiderin laden macrophages. In chondroblastoma, chondroid matrix and plump, spindle-shaped mononuclear cell component along with occasional osteoclastic giant cells are present. In CMF, aspirates show chondroid fragments, spindle-shaped fibroblastic cells and scattered osteoclastic giant cells in a myxoid background. NOF yields groups and clusters of spindle cells, histiocytic cells with vacuolated cytoplasm and occasional osteoclastic giant cells. The latter two lesions are rare especially in a location like rib. The cytology of brown tumor is similar to NOF with characteristic spindly mononuclear cells, osteoclasts and macrophages. The biochemical investigations point to the diagnosis. Giant cell rich osteosarcoma and MFH are characterized by nuclear anaplasia and abnormal mitotic figures and in the GCT there is no neoplastic osteoid formation which is the most pathognomonic finding of a giant cell rich osteosarcoma. Except for the lack of bony involvement, primary giant cell tumor of soft tissue resembles in all its cyto-histomorphological features its osseous counterpart.[2-4]

In general, all GCT's should be considered potentially aggressive and wide excision is recommended.[23]

Fine needle aspiration cytology has been useful in diagnosing similar lesions at rare sites like distal fibula.[7] A primary malignant GCT of sacrum could be identified in a middle aged female[8] as also a multifocal GCT in a skeletally immature patient.[9]

Serum acid phosphatase values are suggested to be a useful marker for diagnosis of GCT of the bone and for evaluation of the efficacy of treatment of the tumor. The values were high in 56% of GCT patients and later decreased to normal values after resection as seen in our case.[10]

To conclude, our case illustrates the fact that giant cell tumors of anterior chest wall can be mistaken for ABC and other malignant tumors of bone and soft tissues. The fine needle or image-guided biopsy would be diagnostic if adequate specimen is obtained.