Diagnostic Work-up and Anesthesiologic Considerations
The diagnostic workup of a goiter begins with simple palpation of the neck and performing an ultrasound. Regarding the former, Pattashanee and colleagues have shown that clinical examination in modified Rose’s position (i.e. , supine, a roll under the shoulders, and by hyperextending the neck) has an excellent sensitivity (98%) and a variable specificity (46.7-91.1%) to identify substernal extension36. Another interesting result is that, in the absence of the Pemberton’s sign, the probability of getting a false positive finding of a substernal extension was only 4%, and this is quite relevant in the context of low-income countries where the availability of CT scan is scarce3633, an 89% sensitivity and 87% specificity for any degree of tracheal narrowing were registered (AUC = 0.90)37.
CT scan of the neck and thorax remains the gold standard for a full assessment and classification of RG because it evaluates the dimensions, the morphology, and the relationships to the adjacent mediastinal anatomical structures (Figure 2 ). It is usually performed with the aid of intravenous iodine contrast agents, despite a theoretical more than a real risk of precipitate thyrotoxicosis (Jod-Basedow phenomenon)5,21. Some authors have proposed a simple yet not validated rule-of-thumb: if the RG remains cranial to the aortic arch in the sagittal plane of CT performed while the patients maintain a full neck extension, then sternotomy is usually not necessary38. Classical predictors of the need for sternotomy are based on the craniocaudal length of the retrosternal extension, the ratio between the retrosternal portion and the diameter of the upper thoracic inlet (so-called “iceberg” or “cone-shaped RG”), and the anterior or posterior relationships with major vessels2,393 had a negative predictive value for the extra-cervical approach of 100%40. Volume was manually outlined on axial sections by two radiologists, but interrater agreement and kappa coefficients were not calculated thus leaving doubts on the applicability of this technique. The value of imaging in the prediction of an exclusive transcervical approach to RG will be discussed further in the next sections.
CT scan lets a clear assessment of both tracheal deviation and extrinsic compression, which are both reasons why airway management is usually labeled as difficult in RG patients, and a very low threshold for endoscopic-assisted awake intubation is kept by anesthesiologists. This fear mostly derives from anecdotal evidence of extreme RG where emergency tracheostomy29, or the need for a pediatric flexible bronchoscope were necessary41. In the most extreme case, the application of extracorporeal membrane oxygenation (ECMO) before the induction of general anesthesia has been described with success42,43. Actual evidence instead dispels the myth of a difficult airway, in the absence of classical risk factors (mouth opening less than 4 cm, a thyromental distance less than 6 cm, Mallampati Class III or higher, etc.)39. In a 2020 paper, 22 cases of “giant” type I RG (defined as trespassing the aortic arch on CT scan), with a mean maximum diameter of 114.2 ± 19.5 mm were all successfully intubated with standard laryngoscopy or awake tracheal intubation (for 5 patients, 22%) using flexible bronchoscopy44. A larger multi-institutional series from the USA, confirmed that direct laryngoscopy or videolaryngoscopy techniques were sufficient in 162 patients (90.5%), while transnasal of transoral fiberoptic was intubation used for the remaining 17 patients45. The authors did not give a clear-cut definition of RG, yet they performed a multivariate analysis where the body mass index was the only factor to positively correlate with the number of attempted intubations45.