INDICATIONS

The transcervical approach to thymectomy (TCT) is almost exclusively reserved for nonthymomatous myasthenia gravis (MG). TCT is an attractive surgical option because it is the least invasive approach for an operation to treat generalized weakness with the lowest reported rate of postoperative myasthenic crisis, the single most concerning disease-specific morbidity. Detractors of TCT argue that this less invasive technique limits the complete resection of thymic tissue. There are no prospective randomized comparisons between thymectomy and medical therapy, and none between the various approaches to the procedure.

The practice guideline of the American Academy of Neurology regards thymectomy as “an option to increase the probability of remission or improvement” of MG. Complete remission and clinical improvement of symptom severity have been reported in multiple observational studies: These provide the basis for selective resection of the gland. Thymectomy for purely ocular MG is not supported by some neurologists; however, about one half of these patients later progress to generalized MG; early thymectomy may reduce this proportion.

By inference, thymectomy is also an option in other immunologic disease associated with thymic hyperplasia, aplastic anemia for example.

TCT has been reported for the resection of selected, small thymomas, an indication not favored by the author.

TCT may be selected for resection of an intrathymic parathyroid. The resection of parathyroid adenoma, known or suspected to be located within the mediastinal thymus, has been recommended at the time of neck exploration, particularly when less than four glands are found.

CONTRAINDICATIONS

Antecedent sternotomy leaves planes obliterated on which the execution of this operation depends. Prior tracheostomy or neck exploration create obstacles, but do not preclude TCT.

Thymoma, however small or favorable in location, is not an appropriate target for the cervical approach, no matter whether associated with MG.

Emergent thymectomy for severe MG with respiratory impairment is inadvisable due to the high risk of postoperative respiratory failure.

Antecedent cervical vertebral operations may lead to severe restriction in the range of neck extension and obstruct the surgeon’s view. A different approach should be selected in these patients.

PREOPERATIVE PLANNING

The diagnosis of MG is considered in patients with muscle weakness and easy fatigability and must be secured by at least one or all three of the following tests: Presence of acetylcholine receptor antibodies in peripheral blood, a positive edrophonium chloride (Tensilon) test, or characteristic electromyographic findings in extremity muscles.

The operation has no role in the management of acute, severe MG since postoperative results as measured in remission or improvement evolve one or more years after thymectomy. Symptoms of MG should be controlled before thymectomy with cholinesterase inhibitors, with or without addition of immunosuppressive agents. In preparation for thymectomy, neurologist and surgeon should mutually consider the prevention of postoperative myasthenic crisis. The incidence of myasthenic crisis after TCT is reported as 0.7% to 1%, the lowest of all operative approaches. Intravenous immunoglobulins (IVIG) or plasmapheresis should, therefore, be administered before the operation only to selected patients at increased risk of respiratory failure.

To evaluate respiratory muscle function, forced vital capacity (FVC) is useful as a simple test suitable for bedside comparison early after operation. An FVC of less than 15 to 20 mL/kg, a value extrapolated from other conditions, predicts postoperative respiratory failure. The most sensitive test of clinical respiratory fatigability, however, is the maximal breathing capacity (MBC) measured as the product of frequency and volume of breaths during 1 minute. An impaired MBC may initiate the preoperative administration of IVIG or plasmapheresis, although the precise indication for either treatment in TCT has not been studied.

In every patient undergoing thymectomy for MG, the absence of thymoma should be confirmed either with chemical shift magnetic resonance imaging or computed tomography. In the surgeon’s office, neck mobility and maximal extension are tested to ensure exposure of the mediastinum during operation. The anesthetic team must be aware of the underlying diagnosis to plan the respiratory management of MG and avoid depolarizing muscle relaxants. Following IVIG administration and immediately before operation, a complete blood count is repeated to exclude hemolytic anemia.

SURGERY

The description follows the technique of Cooper et al.

Positioning

Correct positioning of the patient on the operative table is critical to surgical exposure and thus to the success of the operation. The patient is placed supine and the crest of the head is flush with the top of the table. The arms are padded and tucked at the patient’s side. An inflatable bag is placed underneath the shoulders. Once anesthetized, the patient is intubated with a single-lumen endotracheal tube. The operating table is turned 90 degrees counterclockwise and the shoulder bag is inflated to achieve maximum neck flexion while the head remains supported on a head rest. Neck, chest, and upper abdomen are included in the sterile field.

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