Substernal Thyroid Biopsy Using Endobronchial Ultrasound-guided Transbronchial Needle Aspiration

Summary

Substernal thyroid lesions are common, and need to be differentiated from malignancy. Obtaining percutaneous fine needle biopsy is not possible due to its retrosternal location. This article proposes a protocol for biopsy of substernal thyroid lesions using Endobronchial Ultrasound-guided Transbronchial Needle Aspiration (EBUS-TBNA).

Abstract

Substernal thyroid goiter (STG) represents about 5.8% of all mediastinal lesions¹. There is a wide variation in the published incidence rates due to the lack of a standardized definition for STG. Biopsy is often required to differentiate benign from malignant lesions. Unlike cervical thyroid, the overlying sternum precludes ultrasound-guided percutaneous fine needle aspiration of STG. Consequently, surgical mediastinoscopy is performed in the majority of cases, causing significant procedure related morbidity and cost to healthcare. Endobronchial Ultrasound-guided Transbronchial Needle Aspiration (EBUS-TBNA) is a frequently used procedure for diagnosis and staging of non-small cell lung cancer (NSCLC). Minimally invasive needle biopsy for lesions adjacent to the airways can be performed under real-time ultrasound guidance using EBUS. Its safety and efficacy is well established with over 90% sensitivity and specificity. The ability to perform EBUS as an outpatient procedure with same-day discharges offers distinct morbidity and financial advantages over surgery. As physicians performing EBUS gained procedural expertise, they have attempted to diversify its role in the diagnosis of non-lymph node thoracic pathologies. We propose here a role for EBUS-TBNA in the diagnosis of substernal thyroid lesions, along with a step-by-step protocol for the procedure.

Introduction

Substernal thyroid goiter (STG) is a slow growing tumor, eventually causing symptoms in 70-80% of cases. As per literature review, between 2.5-22.6% of STG can have malignant transformation². Compression of the trachea, esophagus, recurrent laryngeal nerve, and superior vena cava often causes symptoms like dyspnea, stridor, cough, dysphagia, dysphonia, vocal cord paralysis, Horner’s syndrome, superior vena cava syndrome, and cerebral edema. Occasional cases of overt hyperthyroidism have also been reported. A retrospective study by Shin et al. reported a positive correlation between thyroid size and presence of shortness of breath, globus sens....

Protocol

The protocol outlined below follows the guidelines of the institution (Roswell Park Cancer Institute, State University of New York at Buffalo, NY).

1. Initial Preparation

1. Perform Endobronchial Ultrasound-guided Transbronchial Needle Aspiration (EBUS-TBNA) under moderate sedation, monitored anesthesia care (MAC), or deep sedation and general anesthesia.
   NOTE: Patient surveys show favorable satisfaction scores with moderate sedation¹⁹, but recent data shows higher diagnostic yield using general anesthesia²⁰.
2. Optionally, perform the procedure without an airway device under moderate sedation. U....

Results

Endobronchial Ultrasound-guided Transbronchial Needle Aspiration (EBUS-TBNA) biopsy of substernal thyroid has been reported in eight case reports as per literature review^12-18. The first case of substernal thyroid biopsy using Endobronchial Ultrasound was reported by Rosario et al. in 2006¹², wherein a CT chest done for metastatic work-up of prostate adenocarcinoma showed mediastinal lymphadenopathies. EBUS-TBNA of the lesion revealed a previously undiagnosed papillary thyroid carcinoma met.......

Discussion

Substernal goiter was first described in 1749 by Haller²³. The reported incidence of substernal or mediastinal goiter varies between 0.2% and 45% of all goiters, depending on the definition used²⁴. More than ten definitions of substernal goiter have been proposed. By the simple clinical definition, a part of the substernal thyroid remains permanently retrosternal on physical exam without neck in hyperextension, as opposed to with neck in hyperextension as per Torre’s definition²⁵. K.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
7.5-MHz Convex Probe-EBUS bronchoscope
Dedicated 22 or 21 G TBNA needle
Ultrasound processor unit
On-site cytopathology (optional)
Moderate sedation drugs - benzodiazepines or fentanyl
Deep sedation / General anesthesia drugs - propofol or remifentanil
Local anesthesia (for airways) - 1% or 2% lidocaine