Carotid body tumors: objective criteria to predict the Shamblin group on MR imaging

Abstract

Background and purpose: MR imaging is an established method for diagnosis and surgical planning of carotid body tumors (CBTs). However no studies have elaborated preoperative objective criteria to predict the Shamblin (surgical) classification of CBTs, an important predictor of vascular morbidity. The purpose of this study was to establish criteria to accurately predict the Shamblin group on preoperative MR imaging for a uniform reporting system.

Materials and methods: MR images of 9 CBTs in 8 consecutive patients who underwent surgery between 2004 and 2007 were reviewed at a tertiary cancer hospital. The surgical records were blinded to the radiologists. A radiologic classification into 3 types (I, II, and III) based on the maximum degree of circumferential contact of the tumor with the internal carotid artery (ICA) was attempted and correlated with the Shamblin group in surgical records.

Results: There were 5 type III, 3 type II, and 1 type I tumors. The type I tumor had an ICA maximum circumference of contact less than or equal to 180 degrees , type II tumors had more than 180 degrees and less than 270 degrees , and type III tumors had a maximum circumference of contact of 270 degrees of more. MR imaging accurately predicted the Shamblin group in 8 (100%) of 8 operated tumors. Tumor size and Shamblin group did not have a uniformly predictable relation.

Conclusions: Shamblin group can be predicted preoperatively on MR imaging, and the maximum degree of circumferential contact of the CBT with the ICA on axial images is the criterion to predict the Shamblin group.

Fig 1.

Shows a schematic diagram of the Shamblin grouping of CBTs into I, II, and III, as well as IIIb (as proposed in the modification to Shamblin's classification by Luna-Ortiz et al). The surgical grouping is chiefly based on the relationship of the tumor to the carotid vessels, ICA and ECA. The class IIIb tumors include tumors of any size that are intimately adherent to the carotid vessels. The oblique lines shown represent the X and XII nerves, which are intimately related to the tumors and have to be carefully dissected along with the vessels.

Fig 2.

A schematic diagram demonstrating the measurement of the degree of circumferential contact between ICA and the tumor. Two intersecting lines are drawn between the center of ICA and the points of contact of the circumference of the vessel with the edges of the tumor to obtain the angle (A). A, Type I tumor: the angle “A” is depicted between the 2 intersecting lines. B, Type II and III tumors: the angle measurement tool automatically measures the smaller angle (less than 180°) between the intersecting lines. The actual angle A is the difference between 360° and measured angle “a” (360°−a), as shown here.

Fig 3.

Type I CBT. A, Axial T2-weighted MR image showing a left-sided CBT splaying the ICA (arrow) and ECA (arrowhead) anteroposteriorly. The tumor has an angle of contact of 150° with the ICA. B, Sagittal T2-weighted MR image showing the CBT (*) splaying the ICA (arrow) and ECA (arrowhead) anteroposteriorly.

Fig 4.

Type II CBT. A, Axial T2-weighted MR image showing a type II right-sided carotid body tumor (star) splaying the ICA posteriorly and ECA (arrow) anteriorly. The circumferential degree of contact of the tumor with the ICA is the difference between 360° and the measured angle (150°) in the figure, that is, 210°. B, Line diagram illustrating the tumor-ICA circumference of contact of the type II CBT in A.

Fig 5.

A bulky type III CBT. Axial T2-weighted MR image showing a type III right-sided CBT as a brightly hyperintense mass with multiple flow voids. The ICA and ECA are both completely encased (360° circumference of contact).

Fig 6.

Small-volume type III CBT. Axial T2-weighted MR image showing a left-sided CBT (*) with complete encasement of ICA and ECA.