The third vascular route of the inner ear or the canal of Cotugno: Its topographical anatomy, fetal development, and contribution to ossification of the otic capsule cartilage

Abstract

Three vascular routes to the inner ear are known: (a) through the internal acoustic meatus with the vestibulocochlear nerve; (b) from the endolymphatic duct aperture; and (c) along the canal of Cotugno (CC) inserted into the vestibular part of the ear from the superior or brain side. The third is believed to contain only veins. Examinations of 33 human embryos and fetuses at 6–40 weeks demonstrated that (a) the CC appeared as a recess of epidural mesenchymal tissues at the superior aspect of the otic capsule cartilage in embryos and it was inserted deeply to issue multiple peripheral divisions inferolaterally and posteriorly at midterm; (b) the CC consistently passed through a ring of the superior or anterior semicircular canal and contained both, the arteries from the vestibulocochlear nerve origin at the midbrain and the vein draining into the sigmoid sinus or petrosal sinuses; and (c) the CC appeared not to contribute to ossification of the otic capsule cartilage but, after endochondral ossification of the internal ear, woven bone development occurred along a smooth interface of the CC with the ossified ear. In contrast, another interface between the developing bone and the residual cartilage of the otic capsule was rough and wavy with many short bony columns, called osseous globules. In addition, the endolymphatic duct accompanied veins but no arteries. Our results show that the CC is a major vascular route to the vestibular part of the otic capsule cartilage, but its role appears to be limited after ossification.

Fetal development and growth of the fissula ante fenestram in the human ear

“…Later, the active and delayed ossification toward otosclerosis was defined as a sequential process: (a) "osteocyte-mediated absorption" of the (c) proliferation of vessels and production of lamellar bone (reviewed by Merchant & Nadol Jr., 2010). Therefore, the abnormal calcification at the tympanostapedial syndesmosis may be similar to the ossification in and along the subarcuate process, the latter of which was recently described in detail by the present last author (Honkura et al, 2020). The FAF did not contain a woven bone structure in the present specimens.…”

Association between the developing sphenoid and adult morphology: A study using sagittal sections of the skull base from human embryos and fetuses

“…In this context, a bony AP inserted into the cartilaginous AT corresponded to another type of “mosaic” or complex. Moreover, bones at multiple stages of endochondral ossification coexisted, as seen in the temporal bone petrosal portion of late‐term fetuses (Honkura et al, 2020; Michaels et al, 2010). Finally, we did not find the lingula sphenoidalis although it was considered to ossify at 4 month along the lateral aspect of the internal carotid artery (see also the next subsection).…”

Development of the cartilaginous connecting apparatuses in the fetal sphenoid, with a focus on the alar process

“…During this period, human fetuses have a large gap between the cerebrum and the calvaria [ 23 – 25 ]. In contrast, the cranial base is close to the brainstem, thalamus, and hypothalamus [ 23 – 25 ]. This study demonstrated the development of a temporary connecting apparatus from 7 to 14 WD.…”

“…During the fetal period, the peak increase in brain weight occurs between 9 and 18 weeks [22]. During this period, human fetuses have a large gap between the cerebrum and the calvaria [23][24][25]. In contrast, the cranial base is close to the brainstem, thalamus, and hypothalamus [23][24][25].…”