Secondary Substernal Goiters: Surgical Treatment and Challenges

  

    
 
    
No of patients (%)
  
  

    
Overall complications
    
14 (36.84%)
  
  

    
Transient RLN injury, unilateral (tracheomalacia: 1)
    
2 (5.26%)
  
  

    
Transient hoarseness from inflammatory edema
    
3 (7.89%)
  
  

    
Transient hypoparathyroidism
    
7 (18.42%)
  
  

    
Wound seroma (residual cavity)
    
1 (2.63%)
  
  

    
Wound infection (subcuticular)
    
1 (2.63%)
  
  

    
Pathology
    
 
  
  

    
Benign disease
    
29 (76.32%)
  
  

    
Thyroid nodules
    
26
  
  

    
Hashimoto's/ lymphocytic thyroiditis
    
8
  
  

    
Graves' disease
    
3
  
  

    
Plummers' disease
    
1
  
  

    
Toxic adenoma
    
1
  
  

    
Hürthle cell "benign" neoplasm
    
1
  
  

    
Malignant (papillary)
    
9 (23.68%)
  
  

    
TC (+lymphocytic    thyroiditis: 2) 
    
3
  
  

    
TMC (+lymphocytic    thyroiditis: 2) 
    
6
  

Table 2: SSG surgical specimens.

Unilateral RLN microtraumatism with transient vocal cord palsy happened in 2 (5.26%) patients with bilateral SSG. The first was a young patient with Graves’ disease and limited tracheomalacia (“nonsuspended” trachea), who had a difficult intubation and experienced acute respiratory distress and hoarseness after extubation; he was immediately re-intubated and underwent an emergent tracheostomy; he had a hemi-paresis of the left vocal cord and laryngeal edema on urgent laryngoscopy, he fully recovered in the Postanaesthetic Care Unit, and was transferred to the ward. Before discharge on day 6, his tracheostomy tube was replaced with a new “speaking” one; he was freed from the tube on day 25. The second patient suffered mild respiratory distress and hoarseness after extubation, he had rightsided vocal cord hemi-paresis on urgent laryngoscopy, and was treated conservatively (low dose of hydrocortisone, O2 on demand, bronchodilators); he was discharged on day 6, after undergoing a new laryngoscopy that showed improved vocal cord movement.

Symptomatic hypocalcaemia due to transient hypoparathyroidism was observed in 7 (18.42%) patients; only one required initial intravenous administration of calcium glyconate (1 gr of a 10% solution few times per day) for 3 days, all received oral Ca++ or oral Ca++/Vit D (50000-100000 Units per day); six patients needed medication for 2-3 weeks, one required oral Ca++/Vit D for 3 months.

Histology and TG

Histology revealed bilateral nodules in 14 bilateral SSG patients and in all unilateral (SSG side) cases; nodules were identified in the cervical (4 patients), the mediastinal (10 patients) and the cervicomediastinal (21 patients) components of SSGs. Twentynine patients (76.32%) had a benign diagnosis (one intraoperative FNAC result included), while differentiated malignant tumours were identified in 9 (23.68%) patients (Table 2). Lymphocytic/Hashimoto’s thyroiditis coexisted in 12 patients (31.57%), among whom 4 with malignancy (2 TCs, 2 TMCs). Malignancies included papillary TMCs (tumour size <1.0 cm) in 6 patients and papillary TCs with tumour size of 1.2-2.2 cm in 3 patients. All malignancies, apart from 2 TMCs, had developed in the substernal component of the gland. Upon pathologic review, all malignancies were limited to the thyroid gland, with no lesion showing extracapsular invasion. Among patients with high TG value, 2 had TC and 3 TMC (all in substernal component); no one was preoperatively diagnosed. The weight of goiters ranged 85-150 g, with mean 110 g.

Comparison of rates of coexistent malignancy in SSG and surgically treated cervical thyroidopathies.

The results were further compared with regard to malignancy rates. There was a 33.33% rate (32/96) of successful preoperative FNAC result positive for malignancy in the control group, while no one from the SSG group was preoperatively diagnosed. When compared the histology rates of malignancy between the two groups, a preponderance of the SSG group against the control group was documented (23.68% vs 18.08% respectively: p=0.007).

Discussion

Numerous definitions of SSG have been proposed [2-4,8,14]. In the present study we used a less rigid definition with a SSG defined as when any part of the thyroid descends beyond the constant landmarks of the thoracic inlet and the level of the clavicle, radiologically evidenced by CT scan. The SSG is characterized by slow progression and most patients present with palpable neck masses causing remarkable regional deformity and/or compressive symptoms resulting from space-occupying lesions [1,4,9,11,15- 17]. If the adjacent trachea, esophagus, nerves or blood vessels are compressed, the corresponding symptoms would occur: respiratory (dyspnea, wheezing, cough), dysphagia, neurologic (vocal cord paresis, hoarseness, Horner’s syndrome), vascular (superior vena cava syndrome, ischemic attacks), and metabolic (e.g. thyrotoxicosis) [1,4,6,9,10,15,18]. In this study, 38 SSG cases were encountered among 580 consecutive thyroidectomies for various thyroidopathies (6.55%). In our experience, SSGs with unilateral extension were slightly more common than those with bilateral extension (21/17), and right-and left-sided SSGs showed a nearly identical frequency (11/10). All of our patients presented with palpable neck mass and their most common symptom was respiratory distress, which could be exacerbated with raising arms or hyperextending neck (positive Pemberton’s sign [17]).

The CT scan is reported to be the most valuable radiologic investigation for evaluating SSGs with regard to location, extension, anatomical relationships, and the justified choice of the surgical approach [4,9,18-20]. Thyroid function tests help to detect and correct functional abnormalities [1]. FNAC is not recommended because the substernal portion of the goiter is hardly accessible and puncture may lead to hemorrhage or pneumothorax [1,4]. Finally, the vocal cords and their movement can be preoperatively visualized on fiberoptic laryngoscopy.

Most agree that “the presence of a SSG is in itself an indication for surgery”: a long history of having a large SSG precludes neither hyperfunction and malignancy nor complications such as aerodigestive tract compression; 131I to treat large thyrotoxic goiters may precipitate acute reactions that can result in respiratory distress; malignancy occurs in a significant number of these lesions, which may be inaccessible to needle biopsy [1,3,9,10,15,21]. Obviously, conditions such as hyperthyroidism, cardiac arrhythmias and bronchospasm have to be appropriately controlled prior to surgery [1,22]. The present study did not include cases with lesions descending beyond the carina or into the posterior mediastinum, both of which have been proposed as indicators of the need to use a thoracic approach (sternotomy, video-assisted thoracic surgery, lateral thoracotomy) [2,4,7,16,18,23].

TT in SSGs is technically demanding, with greater associated difficulties in blunt dissection of the descending lobe(s) and chances to injury to native structures [8,9,11-14,24-26]. Risks are increased in chronic large SSGs associated with compressive symptoms, and when toxicosis or active thyroiditis coexist [24,25]. For a safe removal of the gland, most investigators propose a primary ligation of the middle thyroid vein and the superior thyrovascular bundle, followed by a meticulous extracapsular dissection of the cervical portions of the lobes, with special attention to preserve the integrity of the posterior (cervical) thyroid, and the mobilization of the descending component(s) by gentle sweeping with the finger along the carotid sheath and the thyroid capsule down into the mediastinum [1]. The ultrasonic knife can deliver fine tissue separation and secure resection and it ensures effective hemostasis within a small surgical space [27].

An issue of paramount importance is the preservation of the native structures in the surgical field of TT for SSG. It is expected that the normal route of the RLN may be altered by the descending spaceoccupying mass [4]. However, the surgical exposure of the RLN during mobilization remains controversial [11,12,20]. Many researchers [27,28] have proposed that, when performing an extracapsular removal in SSG surgery, the RLN should not be routinely exposed; instead, it should be dislocated with the preserved capsule of the posterior thyroid. Others have suggested avoiding blind finger manipulation of a non-accessible inferior aspect of a mediastinal lesion without visual nerve identification and, instead, have recommended adopting a complementary thoracic approach [4,16]. The authors believe that, in the cervical approach, the deliberate dissection of the RLN during an extracapsular TT in SSG cases with accessible inferior aspect, that are commonly associated with mild chronic inflammation in the tracheoesophageal groove, altered anatomy and tracheal deviation, is unnecessary. However, postoperative hoarseness may also be due to transient vocal cord edema or vocal cord injury caused by the endotracheal tube used for anaesthesia [18,24]. The reported frequency of permanent postsurgical RLN palsy in SSGs ranges from 0% to 14.3% [4,6,8,9,18,20]. In the present study, two patients with bilateral SSGs suffered a transient unilateral RLN hemi-paresis (5.26%); only one with Graves’ disease and tracheomalacia required a temporary tracheostomy. Three (7.89%) others experienced mild transient hoarseness that was attributed to vocal cord edema and they were successfully treated conservatively.

Injury or blood impairment of the parathyroid glands leads to postoperative hypocalcaemia [8,13,18,20,27-30]. In a retrospective analysis [8] of 1767 cases with SSG surgically treated in a referral centre for endocrine surgery during a twenty-eight-year period, transient and permanent hypoparathyroidism were encountered in 14% and 4.1% respectively. In the present study, there were 7 (18.42%) patients who suffered transient hypoparathyrodism. Similarly to RLN protection against traumatism, the maintenance of the capsule of posterior thyroid, which permits the preservation of the parathyroids’ arterial branch, is the key to provide a viable gland [13]. If a parathyroid is inadvertently removed, autotransplantation into the sternocleidomastoid is performed.

Another concern is the possible tracheal destruction (tracheomalacia) in chronic large SSGs, that could result in respiratory distress and even in suffocation due to collapse of the tracheal wall following an inattentive extubation [1,22,24,27]. If that happens, then intraoperative tracheal suspension with the patient left intubated for 24-48 hours may be necessary [ 1]. Conventional tracheostomy is not recommended except for the cases with destruction of more than 2 rings in CT scan, tracheal narrowing with difficulty in intubation, or trachea collapse after the tumour removal [27].

Another issue of interest is the better control of the residual cavity, which is left after the removal of a large cervicomediastinal mass [27]. In general, empty body cavities might get soon filled up with reactive serum fluid, that may result in increase of the endo-space pressure, and re-compression of native structures. The authors believe that, in SSG surgery, the vital function of breath is safely protected with the use of negative pressure fine tubes for drainage; these tubes should be extracted later than usual, even in an out-patient setting, and when daily draining is less than 20 ml. We think that such drain secures the required time for healing and functions as an equilibrium that allows smoother cavity shrinkage.

A controversial issue remains the type of surgical removal of SSGs with regard to malignancy. In most studies, the incidence of malignancy among SSGs is increased when compared to patients with cervical nodular goiters, and ranges from 3.7 to 22.6% [4,6,8- 10,14,19,21]. Cancer foci of SSGs are most commonly located in the intrathoracic component [1,4,21]. Also, commonly, malignant tumours are limited to the thyroid gland without extrathyroidal invasion, which should require a combined cervical-thoracic approach [4]. In our study, all SSG malignancies (9 cases, 23.68%) were papillary tumours diagnosed postoperatively, with all of them limited to the thyroid gland. Seven of these cases (3 TCs, 4 TMCs) were located in the substernal component and, thus, they would have been inaccessible to preoperative FNAC. During the same period, we encountered other 98 cases (18.08%) with differentiated thyroid malignancy, who had undergone TT or completion TT for various cervical thyroidopathies, among whom 32 had a preoperative FNAC diagnosis of malignancy which was confirmed postoperatively.

TG level fails to get certain value as a diagnostic screening tool for malignancy. In this study, elevated TG levels in SSG patients undergoing TT constituted an index of suspicion for malignancy, but not always corresponded to thyroid malignancy; on the contrary, patients with normal TG values were found to have TMCs (3) or TCs (1).

On a multivariate analysis [10], substernal location was found to be the only variable independently associated with an unexpected thyroid cancer on surgical pathology. Thus, surgery is not only the most effective treatment for symptomatic patients with SSG, but also gives the definite answer to possible or unanticipated malignancy [4,10,29].

Conclusion

SSG is frequent, representing a 6.55% of all surgically treated thyroidopathies in this study. The descending goiter associated with present or imminent compressive symptoms, mostly respiratory distress, and the risk of malignancy, constitutes a major indication for thyroid surgery. All secondary SSGs not exceeding the aortic arch on CT scan can be approached transcervically. TT is the treatment of choice. With greater care taken during surgical removal, the substernal nature of the goiter does not have major impact on postoperative complications. In this study, the incidence of transient monolateral RLN palsy (5.26%) and transient hypoparathyroidism (18.42%), and the overall morbidity are comparable to the acceptable respective values after TT for cervical goiters. The rate of postoperatively discovered thyroid malignancy in patients with SSG of this study is 23.68%, and it is increased when compared to patients with cervical thyroidopathies (p=0.007). Finally, the elevated TG levels in SSG patients undergoing TT are not always a confirmation of thyroid cancer. Depending on these findings, we suggest that all SSGs should be surgically treated.

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