Running pattern of the internal maxillary artery assessed using arterial-phase CT images in 434 sides in Japanese individuals.

Objective: The internal maxillary artery (IMA) follows two primary running patterns: lateral, where it traverses the superficial layer of the lateral pterygoid muscle, and medial, where it passes through the deep layer. The frequency of these patterns varies among populations, with the medial type reported in 6-18 % of Asians and 37-46 % of Caucasians. Ligation of the IMA, commonly performed during total or partial maxillectomy to reduce bleeding, is more challenging in the medial type due to its deeper anatomical position. Therefore, preoperative identification of its pattern is crucial. This study analyzed the IMA running pattern in Japanese individuals using arterial-phase CT and the diagnostic accuracy of standard contrast-enhanced CT.

Methods: We retrospectively analyzed 434 sides from 217 Japanese individuals who underwent arterial-phase CT. The IMA was classified as lateral or medial based on its relationship with the lateral pterygoid muscle. We evaluated whether the running pattern was influenced by anatomical side, gender, or the side of tumor involvement using Fisher's exact test. In 213 patients, arterial-phase CT findings were compared with standard contrast-enhanced CT.

Results: The lateral and medial types were observed in 94 % (407 sides) and 6.2 % (27 sides), respectively. No significant differences were found between anatomical sides (p = 0.11), gender (p = 0.092), or tumor involvement (p = 0.57), though symmetry was significant (p = 0.003). Standard contrast-enhanced CT showed 97.4 % concordance with arterial-phase CT but misclassified 17 % of medial cases.

Conclusion: The lateral type was predominant in Japanese individuals. Preoperative assessment of the IMA using arterial-phase CT is recommended when standard CT is inconclusive. Accurate identification can improve surgical precision and reduce complications.