July 2024 Medical Image of the Month: Vocal Cord Paralysis on PET-CT
Tuesday, July 2, 2024 at 8:00AM 
Figure 1. Axial image from a CT scan (A) showing a spiculated left upper lobe nodule. An axial image from a more inferior slice, at the level of the left hilum (B), demonstrates prominent left hilar adenopathy filling the AP window/subaortic space (*).
Figure 2. Axial images from an FDG-PET CT obtained shortly after the initial chest CT demonstrates focal hypermetabolic activity associated with the left upper lobe nodule (A) and pre-aortic adenopathy (arrowhead). There is also hypermetabolism associated with the right (contralateral) vocal cord (B) (arrow).
A 60-year-old woman with a past medical history of hypertension, rheumatoid arthritis, and a significant smoking history (40+ pack-years) presented with a 3-month history of hoarseness of voice as well as a 10 lb weight loss over a 5-month period. Chest CT revealed a spiculated left upper lobe nodule (Figure 1A). Additionally, there was evidence of bulky mediastinal and left hilar lymphadenopathy (Figure 1B). A subsequent 17-FDG PET-CT (Figure 2) demonstrated marked metabolic activity in the left upper lobe nodule with an SUV maximum of 9.1. Metabolically active mediastinal and left hilar lymphadenopathy was also noted with an SUV maximum of 5.9.
Interestingly, increased metabolic activity of the right vocal cord compared to the left was noted on the PET scan (Figure 2B). Direct laryngoscopy, performed during intubation for a diagnostic bronchoscopy and endobronchial ultrasound, confirmed left vocal cord paralysis. EBUS sampling of multiple mediastinal hilar lymph node stations, including 4L, and 7, confirmed malignant cells compatible with small cell lung carcinoma. Immunohistochemistry further supported the diagnosis, revealing positive staining for TTF-1, synaptophysin, CD56, and focal chromogranin negativity.
The false-positive PET scan of the larynx, correlated with laryngoscopic findings, points towards contralateral vocal cord paralysis. The asymmetrical FDG uptake in the right vocal cord is attributed to compensatory muscle activation due to left vocal cord paralysis. Vocal cord paralysis is almost twice as common on the left due to the longer anatomical pathway of the left recurrent laryngeal nerve and the fact that it passes through the aortopulmonary window [1]. In this case, PET/CT images demonstrated that the focal FDG uptake was localized in the right vocal cord muscles. This focal FDG uptake is a result of increased work of vocal cord muscles caused by contralateral (left) recurrent laryngeal nerve palsy due to direct nerve invasion by the metastatic adenopathy. Knowledge of this pitfall is important to avoid false-positive PET results [2].
Abdulmonam Ali, MD
Pulmonary & Critical Care
SSM Health
Mount Vernon, IL USA
References
- Lee M, Ramaswamy MR, Lilien DL, Nathan CO. Unilateral vocal cord paralysis causes contralateral false-positive positron emission tomography scans of the larynx. Ann Otol Rhinol Laryngol. 2005 Mar;114(3):202-6. [CrossRef] [PubMed]
- Oner AO, Boz A, Surer Budak E, Kaplan Kurt GH. Left Vocal Cord Paralysis Detected by PET/CT in a Case of Lung Cancer. Case Rep Oncol Med. 2015;2015:617294. [CrossRef] [PubMed]
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