Morphometric Analysis of Lingula Sphenoidalis and Its Surgical Relevance

Background: The lingula sphenoidalis and petrolingual ligament (PLL) are relevant anatomical landmarks when approaching lesions involving the posterior cavernous sinus, Meckel’s cave, and carotid canal. Intimately related to these structures, the PLL runs on the upper border of the carotid canal, between the lingula sphenoidalis and anterior process of the petrosal bone (APP), and represents the posteroinferior attachment of the lateral wall of the cavernous sinus. Given the considerable variability in size and configuration of the lingula sphenoidalis, we sought to define its morphometric patterns and surgical relevance.

Materials & Methods: The region of the lingula sphenoidalis was examined independently by two investigators in 63 dry human skulls (126 sides). For each skull, we measured the length of its sides, height and width at its base, distance between the lingula sphenoidalis and APP (petrolingual line), and orientation of petrolingual line to the Frankfurt line. We then identified four shapes of the lingula sphenoidalis as crest, lamellar, semilunar, and pyramidal. Depth of the carotid canal and distances between lingula sphenoidalis, trigeminal impression, and foramen ovale were identified. Measurements were made in situ with calipers and ruler; data were analyzed (mean ± standard deviation). Inter-rater agreement for individual data was evaluated by weighted Cohen’s kappa (kw ≤ 0.40 = poor; kw 0.41–0.60 = moderate; kw 0.61–0.80 = good; kw < 0.8 = excellent) using SPSS software version 23.0. Length and width of the PLL on the internal carotid artery (ICA) was measured in 5 cadaveric formalin-fixed heads bilaterally dissected through a CT-guided extradural subtemporal approach, after anterior reflection of Meckel’s cave. The angle between the petrolingual line and ICA was measured using BrainLab.

Results: Inter-rater agreement ranged as follows: good to excellent for petrolingual line and orientation relative to Frankfurt line; good to excellent for length of lingula sphenoidalis sides; and poor to moderate for height and width of base. The lingula sphenoidalis was always present for one observer but absent in 3 sides for the other (kw 98%). Inter-rater agreement for fusion rates of lingula sphenoidalis to APP was excellent (kw 97%). The most common shape was crest-type, followed by semilunar and lamellar types (kw 80%). Depth of carotid canal averaged 9.07 ± 2.02 mm. Distances averaged 11.67 ± 2.04 mm between the lingula sphenoidalis and trigeminal impression, and 9.23 ± 1.89 mm between the lingula sphenoidalis and foramen ovale. The PLL was present in all specimens (10 sides); its length on the ICA averaged 5.60 ± 0.92 mm and width averaged 4.70 ± 0.82. When looking at the petrolingual line related to the Frankfurt line, various angulation of the ICA were identified.

Conclusions: Our analysis confirms the diversity of the lingula sphenoidalis, and its varied lengths and shapes. Angulations of the ICA (C3- C4) were influenced by the orientation of the petrolingual line. Anatomical variations of the lingula sphenoidalis and PLL are significant in surgical planning, especially when using PLL as a surgical landmark for identification of the ICA and cavernous sinus.