Teaching Case

A 75-year-old male with an oncologic history of T3N1M0 NSCLC treated with lobectomy and adjuvant chemotherapy and cT4N2M0 recurrent/second primary 7 years later treated with chemo- and immunotherapy underwent surveillance CT chest after being 1 year in remission. Following the CT he mentioned slowly progressive hoarseness with intermittent throat pain.

Contrast-enhanced CT scan of the neck and thorax shows an irregular mass centred on the left thyroid cartilage overcrossing to the right with invasion of strap muscles and the paraglottic region, resulting in medialisation of the left vocal cord (Fig. 1a-c). Bone window shows lytic changes in the enlarged cartilage with sclerosed edges (Fig. 1d-e) Dubious intralesional chondroid calcifications are seen,  DD remaining cartilage “islands”. No lymph node enlargement or signs of mucosal disease in the neck were present. The thoracic part showed known posttreatment changes without signs of recurrence or new disease.

Since differential diagnosis included metastasis as well as primary malignancy like (chondro)sarcoma additional 18-F-FDG PET-CT was performed which showed hypermetabolic activity in the mass without signs of distant metastasis or recurrent lung cancer (Fig. 2).

Final diagnosis has been made with histological sampling by CT-guided bone biopsy after sedation.

Thyroid cartilage is a rare location of hematogenous metastatic spread. This is due to the poor terminal vasculature of this tissue [1]. It has been described in different neoplastic conditions such as multiple myeloma, lung [2], prostate, colon and breast cancer, most of the times in an advanced metastatic stage. Nevertheless solitary metastatic recurrence is possible as our case of a multimodal treated stage III NSCLC illustrates.

Progressive hoarseness is an indication for further clinical evaluation, most of the time endoscopically at first. If no mucosal abnormality is found and vocal cord paralysis has been proven, CT scan of the trajectory of the recurrent laryngeal nerve is the next step. In this case it was an unexpected finding on routine FU imaging during the pandemic COVID era. The patient didn’t mention his complaints which at first were relatively mild without dyspnoea or dysphagia.

Most of the time laryngeal cartilage destruction is caused by direct spread of mucosal disease (laryngeal squamous cell carcinoma). Non-epithelial tumours account for only 2-5% [1] of laryngeal cancer, chondrosarcoma being the largest subgroup. Reports of metastasis to the larynx are mostly in (sub)mucosal location. Key finding in this patient is the identification of the centre of the mass in the cartilage itself with relative mild submucosal spread. Other non-epithelial laryngeal tumours like schwannoma do not involve the cartilage and are more circumscribed.

CT can help in analysing the cartilage and MRI can more easily visualize the soft tissue extension and characterize by identifying signal intensity differences. Differentiating primary laryngeal cartilage neoplasm from metastasis by CT/MR imaging alone is not feasible. Indirect evidence by dissemination study like (PET)-CT helps in raising odds, but does not rule out metastasis in solitary disease location.

Initial endoscopic biopsy sampling was false negative with only reactive stroma changes found.  Literature reports emphasize the need for adequate histological samplings [3]. Histologic biopsy with PET-CT correlation led to the final diagnosis.

In our tumour board meeting it was decided to irradiate the lesion, since laryngectomy with definitive tracheostoma, which would be first-choice treatment, was found to be too mutilating in this palliative setting without improving the long-term outcome and taken into account the relatively mild clinical course.

Our teaching point is illustrating the possibility of metastasis in the thyroid cartilage, especially if the patient has an oncological history and clinical examination is without signs of mucosal disease.