This study is to our knowledge the first one to present the cartilaginous anatomy of the LLJ between the lateral crura of the LLCs and the ULCs using micro-MRI. The medial and lateral crura of the septolateral cartilages were classically considered as two separate cartilaginous structures (respectively ULC and QC), until their continuity was recently demonstrated using micro-MRI [3]. In the present study, we did not find any continuity between the ULC and the LLC. Moreover, the morphological aspect of their connection was highly variable, with only 1/8 (12.5%) of the LLJs corresponding to the classical anatomical description of a scroll articulation (inter-connected roman tiles). Finally, we did not individualize any ligament or sesamoid cartilage adjacent to the LLJ, but posterior accessory cartilages in 75% of the cases.
In contrast to classical concepts, the Evo-Devo theory supposes that the embryological intermaxillary process give rise to the septolateral cartilages and the embryological lateral olfactory processes to the lower lateral cartilages [7, 14]. Starting from the beginning, the olfactory placodes that appear by the fifth week on the embryo’s head invaginate to form two olfactory wells, their superficial margins being then vertically separated into two hemi-circumferences called lateral and median olfactory processes. The two median olfactory processes then fuse on the midline to form the intermaxillary process, which invaginates itself, and by the way attracts the two lateral olfactory processes in front of him, without merging of the latter. The septolateral cartilages then develop themselves from the intermaxillary process, while the LLCs develop from each lateral olfactory process. LLCs and septolateral cartilages stay connected together and to the olfactory mucosa, and suspended to the skull base via a continuous fibrous membrane, the olfactory fascia, which develops from the olfactory pits’walls and seems to invaginates into the pyriform aperture [15].
Our micro-MRI study did not individualize within the olfactory fascia any “radiological” ligamentous structure, especially between the LLCs themselves and between LLCs and ULCs, unlike Daniel and Palhazi [12]. It is however worthy to notice that the term “ligament” refers to “a band or sheet of fibrous tissue connecting two or more bones, cartilages or other structures”, leading to a broad definition [12, 16]. To date, the description of the “cartilaginous nose” was based only on anatomical dissections [6, 8, 9, 12, 17, 18], inducing a risk of fragile soft tissue distortion. Moreover, even during anatomical dissections, some tissues are difficult to precisely characterize, and it is therefore unclear if the described inter-domal ligaments truly correspond to ligaments, or fibrous or aponeurotic tissue. The results of our study support the fact that the answer to the aforementioned question is truly moot. In the author’s surgical experience of septo-rhinoplasty by disarticulation [11], the surgical dissection aims to preserve the olfactory fascia continuity and its attachment to the skull base, but do not rely on the hypothetic presence of ligaments.
We could individualize accessory posterior cartilages in 75% of the cases, as described by Daniel and Palhazi [12]. The origin of these accessory cartilages is unsure and debated (16,17). In the evo-devo theory [7, 19], they may represent a fragmented cartilaginous differentiation at the level of continuity between the medial and lateral olfactory processes that will develop into the septolateral and alar cartilages. Their presence supports the olfactory fascia concept (13) saying that the human fibrocartilaginous nose is one continuous structure inserted into the piriform aperture that stays connected to the ethmoidal skull base.
In several surgical procedures, nasal tip rhinoplasty draws on bilateral latero-lateral disarticulation with or without resection of the cephalic border of the lateral crus of the LLC to raise the tip of the nose. The “scroll area” is of capital importance as its reconstruction directly influences surgical outcomes [20]. The presence of a cartilaginous continuity between the lateral crura of the ULCs and LLCs, even partial, could influence the success of this procedure. According to our findings and the Evo-Devo theory, absence of a cartilaginous continuity might be the rule, but larger confirmatory studies are required. Drumheller, in 1973, anatomically described three distinct variations between the cartilaginous LLJ (i.e., joining, alar over-riding and curling), but our study showed mixed patterns of curling, with different amounts of joining and over-riding. A connection between two hook-shaped cartilages clinging together might result in a higher rigidity and robustness than a simple fibro-cartilaginous continuity. We observed only one specimen with this kind of anatomical configuration in our specimens, but its occurrence in the general population remains unknown. We hypothesize that this kind of LLJ could explain the surgical difficulty in some surgical cases to raise the tip of the nose or an asymmetric raise in some patients (this finding was unilateral in our specimen). MRI imaging of the LLJ before surgery may be studied in the future to evaluate if it could help to plan surgical procedures involving the tip of the nose. Deep learning image reconstruction methods have been introduced with promising results regarding scan acceleration and significant improvement in image quality [21, 22], suggesting that in the near future, micro-MRI might be available in clinical practice. On another aspect, MRI study about the volumetric segmentation of the LLCs seems promising in order to develop silicone grafts despite, for the moment, technical limitations secondary to nostrils movement during breathing [4].
This study has limitations, especially the small number of specimens evaluated. We could not compare MRI findings directly to anatomic dissections. Concerning quantitative values, ICC were poor for some parameters, especially LLC thickness, but were considered reasonable for other values; however, given the small sample size this must be interpreted cautiously. A biomechanical study would be ideal to investigate the resistance of the different types of connection between those nasal cartilages but seems difficult to envisage. Also, the relation between the type of LLJ and the risk of nasal tip malposition cannot be truly estimated and would need further studies.
In conclusion, our micro-MRI findings suggest that the classical “scroll area” of the nasal laterolateral cartilages does not seem to be the most frequent type. Other presentations in the LLJ could explain surgical difficulties to raise symmetrically the tip of the nose in some patients, highlighting the potential role of pre-operative MRI of the cartilaginous nose.