Chondrosarcoma of the hyoid bone: a case of mistaken identity in the submandibular region

Discussion

Chondrosarcomas are malignant cartilaginous tumours that often present as slow-growing masses most commonly seen in the pelvis, proximal femur, proximal humerus and ribs.15 They are the second most common sarcoma arising from the bone but are not commonly seen in the head and neck region, accounting for only 1%–12% of reported cases. When they do present, they tend to be more commonly seen in the skull base, larynx or maxilla.15

In the head and neck region, chondrosarcomas present as slow-growing, painless masses over the anterior or lateral aspect of the neck. The more insidious nature of growth, alongside lack of other concerning features, can falsely mimic benign pathology and delay presentation or diagnosis, with some cases reporting up to 7 years of growth before presentation.16

Chondrosarcomas tend to present in the fourth to fifth decade of life, although literature describes presentations from 30 to 88 years of age.17 18 Chondrosarcomas have been reported to show a slight male predominance of 1.9:113; however, other reports suggest there is no predominance to either gender.19

Due to the lack of radiation exposure, ultrasound is often used as the first method of investigation. This is an unreliable diagnostic investigation for chondrosarcomas given the lack of detail appreciable and ability to detect calcifications on the scan. In our case, the first ultrasound in 2018 demonstrated no abnormalities despite the symptom of a mass, while the second ultrasound describes the lesion being of unknown aetiology.

Literature describes CT as being the gold-standard imaging of choice for chondrosarcomas often revealing a heterogeneous expansive mass with matrix calcification and, in some cases, destruction of the hyoid bone itself.4 In our case, MRI was done preoperatively and did not describe the features typical of a chondrosarcoma.

MRI provides no further aid in characterisation of the tumour but provides a benefit in preoperative surgical planning given its multiplanar capabilities.20 Typically on MRI, chondrosarcomas show low signal intensity in T1-weighted imaging and high signal intensity in T2.2 21 It can provide benefit over CT in its increased sensitivity to detecting necrosis seen in higher-grade lesions.22

Biopsies make up an important part of the diagnostic approach to lesions. In many cases, the cytological samples were reported as false negatives or inconclusive.2–7 This can be attributed to the small nature of the target site, performing the biopsy without radiographical guidance or aspirating a sample that does not contain atypical cells. In this case, the cytology showed myxoid stoma with rounded cells; in combination with a reassuring MRI of the neck, the diagnosis was that of a more common pleomorphic adenoma. This case shows the limitations of FNAC not aspirating atypical cells, particularly in rarer conditions. The diagnosis of grade 2 chondrosarcoma relied on histological examination of the excisional biopsy.

Histopathological characteristics of chondrosarcomas include increased cellularity, nuclear atypia and hyperchromasia. These characteristics can determine the grade of the specimen.23 Grading of the chondrosarcoma is important for treatment, prognosis and metastatic potential. Differentiating these lesions from normal or benign tissue depends on recognition of the tumour invading the marrow cavity of the bone.

• Grade 1 chondrosarcomas make up the majority of reported chondrosarcomas of the hyoid bone and are only locally aggressive. These tumours closely resemble normal cartilage with some atypical cells.

• Grade 2 lesions contain more atypical cells exhibiting hyperchromasia and binucleated or multinucleated cells. There have been, to the best of our knowledge, seven previous cases of grade 2 chondrosarcoma.

• Grade 3 lesions show hypercellularity with a sparse matrix. Cells are larger and more often multinucleated as they have become further differentiated. Necrosis can sometimes be seen.

The treatment of choice in chondrosarcomas is wide local excision, ensuring negative tumour margins, given the high recurrence rate of these lesions. One paper suggests that in the case of grade 1 chondrosarcomas, careful curettage alone can be used to treat the lesion.24 Given that the rate of recurrence for chondrosarcomas in the head and neck region is higher than the rest of the body, wide local excision would be preferable to most surgeons.25

There have been cases where radiotherapy has been used in the treatment of chondrosarcomas, although chondrosarcomas are relatively radio insensitive. Radiotherapy can play a part in cases where patients do not wish to have surgery or where the lesion is inaccessible, for example, extending into the skull base.7 It has been described as an adjunctive to wide local excision in several cases, in both grade 1 and grade 2 chondrosarcomas, although the indication for this is unclear.20 In this case, with negative tumour margins, follow-up is sufficient, and MRI would be suitable given its specificity in soft issue pathology and non-ionising nature. This can be performed 6 month postoperatively and then as required, symptom dependent.

In one case, photodynamic therapy was used in a patient declining surgical intervention. While initial postprocedural therapy suggested tumour shrinkage, further follow-up imaging showed subsequent growth in the tumour size for which the patient underwent a further round of therapy. There is no further follow-up on this patient published.26

Prognosis is dependent on tumour grade with an analysis of chondrosarcomas throughout the whole body showed 5-year survival rate of 90% for grade 1, 81% for grade 2 and 29% for grade 3. The most common sites of metastases for chondrosarcomas are the lungs and distal bone.

An important factor is the presence of negative tumour margins post-excision; 83% of patients with negative tumour margins had no recurrence in comparison with 0% in patients with positive tumour margins.26 In light of this, patients should be taken for re-excision if positive tumour margins are reported. Patients should also have long-term follow-up given reports of recurrence several years after primary excision.22