Giant cell tumor of the sellar region
The clinical and radiological impressions were those of a pituitary adenoma (PA) the most common sellar and parasellar lesion. The differential diagnosis of a non-functioning PA is extensive and includes cysts (Rathke's cleft, arachnoid), tumors (craniopharyngioma, meningioma, lymphoma, germ cell and metastatic tumors), aneurysm, granulomatous/inflammatory lesions (lymphocytic hypophysitis, histiocytosis, sarcoidosis, Wegener's granulomatosis) and infections (tuberculosis) [1, 2]. In the present case, the radiological findings and the hormonal levels were consistent with non-functioning PA. However, the clinical course was faster, the patient younger than usual (peak incidence between the 4th and 6th decades of life) and surgical appearance was not that of a PA.
Giant cell tumor (GCT) occurs mainly in the 3rd decade of life, with a slight preponderance in females and is considered a benign lesion, although locally aggressive, with bone destruction and tendency to local recurrence (3, 8). It is classically found in the epiphyses of long bones (distal femur, proximal tibia and fibula, distal radius and ulna) and represents about 2.4% to 5% of all primary bone tumors in adults. It is rarely located in the skull (2%), mostly in the ethmoid and sphenoid bones, particularly in the latter (5, 7). As reported by Weber et al. (7), due to tumor growth in the skull base (mainly in the sphenoid bone), it is not infrequent the destruction of the sella and, consequently, involvement of the pituitary gland, as previously reported on few occasions (6). In this case, there was hyperprolactinemia secondary to stalk compression and, as demonstrated by MRI, the epicenter of the mass is located inside the sella.
Histologically, there are very large multinucleated giant (osteoclast-like) cells, containing numerous nuclei (7,8) The stromal cell (spindle or ovoid, similar to histiocytes) constitutes the true neoplastic cells, from an osteoblastic origin. They stimulate the formation and differentiation of osteoclasts from precursor cells of monocytic lineage indicating that giant cells are in fact reactive and not the neoplastic cells. Stromal cells also induce the formation of reactive bone (9). Malignant forms, with a sarcomatous stroma, mitoses and a predominance of mononuclear over multinucleated giant cells, are not uncommon, and are likely to metastasize to the lungs (3, 8).
Differential diagnosis on morphological basis (with lesions containing giant cells) may be difficult and should include clinical and radiological data. The patient does not have hyperparathyroidism, therefore a brown tumor was discarded. The appearances where not those of a giant cell reparative granuloma (solid aneurismal bone cyst), in which spindle cells in a collagenous stroma predominate and multinucleated giant cells are not so large as in our case. In addition, it is seen in the maxillary, mandibular and short tubular bones of hands and feet and only rarely in cranial bones (4).
This case illustrates that differential diagnosis of non-functioning sellar/parasellar lesions is challenging due to clinical and radiological similarities among them, and that patients harboring large non-functioning sellar lesions without a definitive diagnosis should be operated to have the precise histological diagnosis and the best therapeutic management.
Contributed by Mônica R. Gadelha, Leonardo Vieira Neto, Juliana Malheiros Giorgetta, Paulo José da Mata Pereira, Paulo Niemeyer Filho, Leila Chimelli