Reigner performed the first carotid body tumor (CBT) resection in 1880, though the patient did not survive. In 1889 Albert became the first to excise a CBT without cranial nerve or carotid artery injury, and Scudder was the first to do so in the United States in 1903. Though the days when “many of the contributions to the literature…are based upon a solitary case” have passed, these tumors are still quite rare and most vascular surgeons encounter few in their career. Earlier diagnosis, improvements in technology and technique, and advances in intraoperative management contribute to low perioperative mortality. Despite this, morbidity because of cranial nerve dysfunction remains a concern.
Duplex ultrasound scans show a highly vascular mass that widens the carotid bifurcation. Concomitant carotid occlusive disease may be identified in patients at risk of atherosclerosis.
Fine needle aspiration or open biopsy of a suspected CBT are contraindicated because of the risks of hemorrhage or injury to the carotid artery.
Computed tomography (CT) and magnetic resonance imaging (MRI) scanning can be used to identify a CBT and estimate its size and extent. Proximity to other vital neck structures can be ascertained. CT scanning is particularly valuable in demonstrating the presence or absence of a plane between the internal carotid artery (ICA) and the tumor. CT may assist in the preoperative assessment as to whether the tumor can be removed without disruption of the ICA. Both CT and MRI scanning are useful in determining bilaterality, which occurs in approximately 5% of patients.
Angiography demonstrates the tumor’s blood supply and its relationship to neighboring vascular structures. CT angiography may be preferred over conventional angiography because of the lack of embolic risk. However, angiography has been used in conjunction with peroperative embolization of large tumors and balloon occlusion testing to determine whether the ICA can be ligated during resection, if required and reconstruction is not possible.
Prophylactic antibiotics should be administered. Invasive arterial blood pressure monitoring and intraoperative cerebral monitoring are recommended.
Classification and Surgical Anatomy of Carotid Body Tumors
The normal carotid body lies in the posterior medial adventitia of the carotid artery bifurcation. The blood supply is derived from the external carotid artery (ECA). CBTs vary from reddish brown to pink with a soft, rubbery consistency and have a thin fibrous capsule. They can grow quite large and can envelop local structures or extend to the skull base.
In 1971 Shamblin and associates developed a classification system for CBTs that is still used today ( Table 9-1 ). It is possible to classify the tumor based on preoperative imaging, but the surgeon must always be prepared to shunt or reconstruct the carotid artery. Patients should be prepared for the potential need for vein graft harvest, as well as replacement of the carotid artery at the time of tumor resection.
|Group I||Tumors are small and may be easily dissected from adjacent vascular structures.|
|Group II||The tumor partially surrounds adjacent vessels and is more adherent to the adventitia.|
|Group III||The tumor is densely adherent to and circumferentially surrounds adjacent vascular structures.|
Avoiding Cranial Nerve Injuries
Particularly with Shamblin’s Group II/III tumors, cranial nerve injury may be unavoidable and sacrifice of a cranial nerve may be required to facilitate a complete resection. However, steps should be taken to minimize injury by carefully identifying adjacent cranial nerves. To do so, comprehensive understanding of the regional anatomy is essential.
The hypoglossal nerve (cranial nerve XII) exits the skull base via the hypoglossal canal and courses caudally between the internal jugular vein and the ICA. It passes medially over the ICA and ECA and posterior to the digastric muscle. There may be significant variability in the course of the hypoglossal nerve. Although typically found crossing the ICA and ECA about 2 to 4 cm cephalad to the carotid bifurcation, it can be found as caudal as the bifurcation or sometimes adherent to the posterior surface of the common facial vein. During CBT resection, the hypoglossal nerve is frequently encountered in the fascia overlying the superior aspect of the tumor.
The vagus nerve (cranial nerve X) normally lies in a posterolateral position relative to the ICA, though occasionally it may be found in an anteromedial position, putting it at greater risk for injury. During CBT resection, the vagus nerve may be identified at its junction with the hypoglossal nerve and then followed caudally. As the vagus nerve courses inferiorly, it must be carefully dissected away from its intimate association with the tumor and the carotid artery. The superior laryngeal nerve can be found in the fascia posterior to the tumor. It courses posterior to the internal carotid artery with the external branch lying posterior to the superior thyroid artery. Injury to the external branch may cause impaired phonation and easy voice fatiguability. The recurrent laryngeal nerve courses in the tracheoesophageal groove and is typically well removed from the surgical field. Vocal cord dysfunction may result from vagal trunk injury.
The marginal mandibular branch of the facial nerve (cranial nerve VII) courses along the masseter muscle parallel to the mandibular ramus. It is at risk with retraction deep to the mandible and with an incision that does not course posterior toward the mastoid process.
The spinal accessory nerve (cranial nerve XI) and glossopharyngeal nerve (cranial nerve IX) are at risk during a resection that extends near the skull base. The spinal accessory nerve lies anterior to the most distal portion of the ICA and posterior to the stylohyoid muscle. It should be identified as it enters the sternocleidomastoid muscle. The glossopharyngeal nerve crosses anterior to the internal jugular vein and ICA near the skull base.
The deep fascia of the tumor may be intimately associated with the sympathetic trunk. Sacrifice of this structure during resection may lead to Horner syndrome.
Avoiding Intraoperative Stroke
A “no touch” technique should be used in handling the carotid bifurcation, particularly when atherosclerosis is present. With large tumors, this may not be possible. Heparin is used if carotid replacement is required.
Preoperative embolization may reduce intraoperative blood loss, but improvement in clinical outcome has not been demonstrated. With the possible exception of tumors exceeding 4 to 5 cm in size preoperative embolization is not performed because the risk of embolism outweighs the benefit of reduced intraoperative blood loss.
The use of bipolar electrocautery minimizes risk of injury to adjacent cranial nerves and is of particular value while separating the tumor from cranial nerves. Combined with a meticulous dissection, bipolar electrocautery can reduce intraoperative blood loss.
A rolled sheet should be placed underneath the shoulder to facilitate neck extension. The head should be turned away from the surgical site and placed in a foam ring. The neck, mandible, ear, and upper chest should be prepped. The face anterior to the ear and the entire occipitotemporal region posterior to the ear should be prepped, as well, for the possibility of requiring higher exposure.
A transverse cervical incision is made along a neck crease. As the sternocleidomastoid muscle is approached, the incision is curved cranially toward the earlobe. If higher exposure is necessary, the incision can be extended in a curvilinear fashion posterior to the ear. For younger patients with CBT, we use a “hairline” incision that passes in a craniocaudal direction along the posterior neck ( Fig. 9-1 ). Alternatively, an incision can be made overlying the sternocleidomastoid muscle, extending from just cranial to the clavicular head toward the earlobe as typically performed for a carotid artery exposure.