Introduction

Multinucleated giant cells (MGCs) are larger than normal body cells having a definite morphology and function. They consist of multiple nuclei arranged in specific morphology dispersed in the cytoplasm. MGCs of one type or another are commonly observed in the histopathology of various oral and maxillofacial pathologies.^[1] MGCs were first reported in tuberculous granulomas by Rokitansky and Langhans, over a century ago.^[2] Giant cell lesions (GCLs) are a group of varied lesions that contain a multitude of multinucleated, osteoclast-like giant cells within connective tissue stroma. Conventionally, these are classified as peripheral if they lie within the soft tissue or central if they lie within the jaw bone.^[3]

Mohajerani et al. reported that 6.36% of the oral biopsies received in their lab were multinucleated giant cells containing lesions.^[4] They are easily observed under a microscope and their presence is pathognomonic in certain lesions such as peripheral giant cell granuloma (PGCG) and giant cell fibroma.^{[5, 6]} However, in some lesions they present a diagnostic dilemma because of uncharacteristic histopathological appearance, thus emphasizing a need for exploring clinical, radiological, and other details to arrive at a final diagnosis.^[7-13] Perplexingly, sometimes, the presence of giant cells can just be an additional non-diagnostic finding.^{[14, 15]}

This study aimed to study the prevalence of GCL pertaining to the oral and maxillofacial regions in our department and dissertate GCLs along with the differential diagnosis, special stains, and other investigations, necessary for their characterization and propose a tentative diagnostic scheme for GCLs.

To the best of our knowledge, this is the first case series aimed at ascertaining the role of giant cells as pathognomonic in diagnosis, diagnostic dilemma, or additional findings in oral lesions.

Materials and Methods

In accordance with the Helsinki declaration and relevant guidelines, we queried our records at the Department of Oral Pathology and Microbiology, from January 2018 to June 2019. We included all those cases in this study which revealed giant cells in histopathology and for which appropriate clinical, radiological, and other details were available. These were reviewed retrospectively by the six pathologists and were classified according to a working classification followed at our department. This classification was based on whether giant cells were diagnostic, coexisting with some other lesion (hybrid lesion), creating a diagnostic dilemma, or were just a supplementary finding with no role in diagnosis (Table 1). We excluded cases with insufficient information about the history, clinical photographs, radiological imaging, and other relevant investigations.

Results and Discussion

Our search revealed 25 lesions among 1000 consecutive cases, where giant cells were pathognomonic while an additional 8 cases showed giant cells as a supplementary finding. Intra-osseous giant cell lesions in the order of frequency were central giant cell granuloma (11 cases), cherubism (4 cases), hyperparathyroidism (2 cases), and tubercular osteomyelitis (1 case). Peripheral giant cell lesions included peripheral giant cell granuloma (2 cases), microbial giant cell lesions (2 cases: 1 case of tuberculosis and histoplasmosis each), orofacial granulomatosis (1 case), and 2 hybrid lesions. Out of these 25 patients, eighteen were males and seven were females aged 10-70 years (Table 2). One case of each diagnosis, presenting with characteristic clinical, radiology, and/or histopathology is discussed below.

Cases

• Lesions where giant cells were pathognomonic

• Central giant cell containing lesions

Case 1: A 52-year-old male patient was presented with swelling in the mandibular anterior region of the jaw for 1 year and 6 months. On examination, there was bony hard swelling extending from the 35^th to 46^th region.  Orthopantomogram (OPG) revealed extensive radiolucent lesion ballooning out from the lower border of the anterior mandible. A provisional diagnosis of central giant cell granuloma and ameloblastoma was considered. Microscopy revealed compactly arranged fibrovascular stroma consisting of the abundant spindle to stellate-shaped fibroblasts with interspersed numerous multinucleated giant cells (4-20 nuclei), dense bundles of collagen fibers, and numerous endothelial-lined budding capillaries (Figure 1).

Investigations: Serum PTH, calcium, phosphorus, and alkaline phosphatase were within normal limits.

Differential diagnosis: Histopathological differential diagnosis of central giant cell granuloma, brown tumor of hyperparathyroidism (HPT), aneurysmal bone cyst, cherubism, and giant cell tumor (GCT) were considered.

GCT is a benign but locally aggressive tumor of stromal cells that occurs mostly in long bones and rarely in jaws. Histopathologically, it shows a uniform and diffuse distribution of macrophages and osteoclast-like giant cells with relatively more nuclei in the background of stromal mononuclear cells. These cells can occasionally show increased mitosis, however, usually there is no marked atypia.^[5] The lack of such features eliminated the possibility of GCT. Normal PTH and calcium levels in the present case excluded hyperparathyroidism. Cherubism occurs at a young age with symmetrical bilateral involvement of jaws thus it was excluded. An aneurysmal bone cyst is characterized by large sinusoidal spaces lined by connective tissue with a focal distribution of MGCs. Surgical notes are very important for the diagnosis of this entity which revealed a blood-soaked sponge appearance.^[6] Further, as the present case did not show necrosis, increased mitosis, abnormal mitosis, and cytological atypia, the malignant giant cell tumor was excluded. After ruling out all of these lesions, a final diagnosis of central giant cell granuloma (CGCG) was given.

Case 2: A 10-year-old female was presented with swelling in right and left cheek region giving a cherubic appearance that had grown slowly in the last year. On examination, there was diffuse bony hard swelling in the mandibular alveolus and bilateral rami. Orthopantomogram revealed a mixed radiolucent-radiopaque lesion in the bilateral rami of the mandible with mixed dentition. CBCT scan showed similar features as in OPG with a developing lesion in the right maxillary molar region. Bilateral incisional biopsies revealed loose to dense fibro cellular stroma showing perivascular eosinophilic cuffing, multinucleated osteoclastic giant cells with minimal inflammatory infiltrate, few myxomatous areas, and reactive osteoid formation lined by osteoblasts (Figure 1). All other giant cell lesions were excluded based on young age and bilateral mandibular presentation. So, the final diagnosis of cherubism was confirmed.

Case 3: A 37-year-old lady was presented with multiple multilocular lesions on the bilateral mandible and clivus region. CECT and PNS view showed an expansile multiloculated cystic lesion with inner body destruction noted in the body of the right and left mandible with bone remodeling and thinning of the inner cortex adjacent to 1^st and 2^nd molar teeth. MRI revealed another lesion in the anterior part of the clivus bulging into sphenoid sinuses with thinning of diaphragmatic sellae. Microscopy from left and right mandibular lesions and a clival tumor revealed compactly arranged fibrovascular stroma intermixed with numerous multinucleated giant cells. Intervening stroma shows abundant hemorrhagic areas and focal sinusoidal spaces. Few areas show active osteoid formation in the form of trabeculae in varying stages of maturation with osteoblastic rimming (Figure 2).

Investigations: Serum parathormone (PTH) levels were found to be high (81.1pg/ml) but serum calcium was normal.

 Differential diagnosis: Histopathological differential diagnosis of hyperparathyroidism, aneurysmal bone cyst, and hybrid lesion of ossifying fibroma with giant cell granuloma were considered. Due to multiple lesions in the mandible and skull, polyostotic fibrous dysplasia was also considered. The radiology of the case did not show well circumscribed mixed radiopaque-radiolucent lesion thus ruling out ossifying fibroma with giant cell granuloma. Similarly, the absence of peau-d'orange appearance in radiology and the absence of the Chinese letter appearance of woven bone in histopathology ruled out polyostotic fibrous dysplasia.

On the basis of multiple osteolytic lesions and high PTH levels, the final diagnosis of hyperparathyroidism-related brown tumor was established.

• Peripheral lesions

1. Microbial giant cell lesions

Case 4: A 42-year-old male was presented with a painless ulcer on the right retromolar trigone of 3 months. On examination, there was an enlargement of the right submandibular lymph nodes, which were matted and firm in consistency. A provisional diagnosis of traumatic ulcer and differential diagnosis of tubercular ulcer and malignant ulcer was considered. MRI revealed an enhancing lesion in the right masseteric space involving the right medial pterygoid muscle. Microscopy revealed hypercellular stroma showing multiple focal areas of collection of inflammatory cells intermixed with multinucleated giant cells resembling Langhans giant cells surrounded by a zone of fibrosis. High power showed the presence of 7-15 nuclei in the giant cell, histiocytes, lymphocytes, and plasma cells within the granuloma-like areas, and abundant blood vessels with perivascular inflammatory infiltrate primarily composed of plasma cells (Figure 3).

Other investigations: Ziehl Neelsen staining was negative for any mycobacterium. PAS stain was unremarkable.

Differential diagnosis: Presence of granulomatous inflammation histopathologically excluded traumatic and malignant ulcers. Histopathological differentials were tuberculosis, sarcoidosis, foreign body granuloma, and fungal granulomatous inflammation. The absence of a foreign body in histopathological sections and no foreign body giant cells ruled out foreign body granulomas. The lack of multisystem involvement, absence of eosinophilia, and normal Angiotensin Converting Enzyme (ACE) levels were unsupportive of sarcoidosis. Fungal granulomatous inflammations were excluded by negative PAS staining and the non-visualization of fungal organisms. The final diagnosis of tuberculosis was suggested in view of histological findings, epidemiological preponderance, and positive culture reports.

The patient was referred to a pneumologist for further examination and management. Mantoux test, culture tests, and interferon-gamma assay were positive for M. tuberculosis. The patient was started on a standard anti-tubercular regimen. The patient was kept on regular follow up and complete healing of the lesion was observed on follow-up (Figure 3).      

2. Peripheral reactive giant cell containing lesions

Case 5: A 23-year-old male was presented with growth in the left retromolar region for 6 months. A gross examination showed a well-circumscribed lesion with a nodular cut surface. Histopathology revealed parakeratinized stratified squamous epithelium encircling a loose fibro-angiomatous stroma with aggregates of MGCs separated by a band of normal fibro collagenous connective tissue. High power showed multiple aggregates of MGCs containing 5-12 nuclei within eosinophilic cytoplasm, active fibroblasts, dilated and engorged blood vessels and intense chronic inflammatory cell infiltrate. The diagnosis of peripheral giant cell granuloma was given (Figure 3).

• Giant cells creating diagnostic distress/ hybrid lesions

Case 6: 51-year-old male with diffuse swelling on the right side of the mandible. There is a history of two cyst enucleation and extraction of 48^th tooth in 2005 and 47^th in 2012. On examination, there was diffuse swelling on the mandible angle, body, and ramus region causing obliteration of the lower buccal vestibule intraorally. Microscopy revealed the sporadic presence of hyperplastic stratified squamous epithelium of variable thickness showing multiple areas of separation from underlying moderately collagenous capsule. Few areas show basilar budding as well as focal basal palisading within the epithelium. One separate tissue shows a dense presence of histiocytes, multinucleated giant cells, and endothelial cells proliferating into the underlying stroma. High power reveals histiocytes displaying nuclear hyperchromatism and pleomorphism in a few areas. These cells were immunopositive for CD68 and immunonegative for p40, Pan-CK, and p53. The ki67 proliferation index was found to be low (Figure 4).

Differential diagnosis: As the lesion was highly cellular so differentials of squamous cell carcinoma and histiocytic sarcoma were considered. A low Ki67 index was indicative of benign behavior and CD68 positivity suggested histiocytic cells. The final diagnosis of Odontogenic keratocyst with giant cell granuloma was given.

Giant cell lesions, though commonly encountered in pathologies of the oral cavity, have not been explored systematically with respect to their diagnostic significance. A literature search to date revealed either case reports of single giant cell lesions or case series of one particular type of giant cell lesions. To the best of our knowledge, there is no study describing case series of multiple giant cell lesions together with the emphasis on differential diagnosis and approach for diagnosing these lesions. Individual case reports are of limited assistance to the pathologist challenged by a giant cell lesion. Hence, the need for a systematic algorithm, aimed at a diagnostic approach toward giant cell lesions, cannot be overstated. The frequency of GCLs in our institute was 2.3% whereas Mohajerani et al. reported around 6.2% of GCLs in Iran.^[4] This epidemiological difference may be attributed to regional variability in the prevalence of these lesions or the submission of biopsy material to pathologists.

The GCLs are histologically classified into peripheral and central giant cell lesions to further narrow the differentials (Figure 5). Giant cell-rich lesions of bone, also termed central lesions, encompass morphologically diverse tumors of the skeleton. Literature findings of these central lesions reported within jaws are tabulated in Table 3.

These include central giant cell granuloma, giant cell tumor, cherubism, brown’s tumor of hyperparathyroidism, and malignant giant cell tumor. Common to them is CGCG which is a non-neoplastic reparative granuloma where osteoclastic giant cells are distributed within the fibro-cellular stroma.

The present case of CGCG (Case 1 (Figure 1)) is a classic case but no history of trauma is present which is almost always associated with CGCG. The giant cell component may be present in reaction to a recent hemorrhage and a fibroblastic component may represent the older or healing part of the lesion.^[7] The exact origin of giant cells in giant cell granulomas remains unclear. The proposed cells of origin for these giant cells include osteoblasts, mononuclear cells from the phagocytic system reacting to hemorrhage, endothelial cells, spindle-shaped mesenchymal cells (reactive population), foreign body cells, and osteoclasts.^[8]

The closest mimic of CGCG histopathologically is Brown’s tumor. Additionally, the latter shows multifocal lesions, increased parathormone, hypercalcemia, and hypophosphataemia.^[9] Ultrasound, CT scan, or technetium scan techniques can also be used to detect the diseased parathyroid gland.^{[9, 10]} Case 3 in the present study shows multiple osteolytic lesions in the mandible and clivus with histopathology of giant cell granuloma and prominent areas of hemorrhage. An increase in serum PTH levels favored the diagnosis of Brown tumor of HPT. Thus, it is strongly recommended that CGCG should be a diagnosis of exclusion and must be inspected for primary HPT.

Another differential diagnosis of intraosseous giant cell lesions is Cherubism. It is characterized by symmetrical enlargement of jaws limited to the mandible and maxillary bones. It is inherited as an autosomal dominant trait with a mutation in the SH3BP2 gene. SH3BP2 plays a role in regulating the increased osteoblast and osteoclast activities that are seen in normal tooth eruption, and point mutations in the gene could cause pathologic activation of multinucleated osteoclasts, thus causing features of osteolysis and multiple unerupted teeth.^[11] Our case (Case 2 (Figure 1)) was a classic case of cherubism presented in a 10-year-old female, with bilateral symmetrical lesions on the mandible, multiple unerupted teeth, and giant cells in histopathology.

Giant cell lesions (GCLs) are further histologically classified into peripheral lesions which are the ones occurring in the gingiva, buccal mucosa, and tongue. The most common lesion occurring in this location is PGCG which is quite distinct with peaks in incidence during the mixed dentitional years and in the age group of 30–40 years. There is also a growing opinion that giant cells in PGCG may simply represent a reactionary component of the lesion and are derived via bloodstream from bone marrow mononuclear cells. They may be present only in response to an as-yet-unknown stimulus from the stroma.^[12] The origin from osteoclasts remaining from resorption of deciduous teeth explains its commonest site anterior to permanent molars.^[11] Other GCLs that can occur in this location are bacterial, fungal, and foreign-body granulomas. Tuberculosis is the most common chronic bacterial infection, in this part of the world, according to epidemiological studies. The etiologic agent of tuberculosis, M. tuberculosis, is clinically one of the most common microbial causes of granulomas. While caseating granulomas are the classic finding in cases of tuberculosis, they are not always present; non-caseating granulomas may also occur.^[13] Our case (Case 3 (Figure 2)) showed non-caseating granulomas. Special stains like ZN stain are used to see bacilli in the sample. Our case revealed negative ZN staining which is concurrent with the observations that acid-fast bacilli could be reliably demonstrated in only 27-60% of cases, owing to the scarcity of bacilli in the tissue.^[6]