Cerebral spinal fluid (CSF) rhinorrhea occurs secondary to lateral skull base pathology
and defects created by trauma, congenital defects, neoplasms, and iatrogenically.
Refractory CSF rhinorrhea from a lateral skull base source is most commonly managed
via open surgical approaches. The approach for repair is dictated by the location
of the skull base and dural defect. The common pathway, however, is through the eustachian
tube (ET). Given the advances in endoscopic surgery, endoscopic endonasal eustachian
tube obliteration (EEETO) and endoscopic lateral skull base approaches have been utilized
successfully to seal the common pathway for CSF rhinorrhea (Lemonnier et al, Am J
Rhinol Allergy, 2017; Deep and Weisskopf, Otol Neurotol, 2017). While the anatomy
of the ET has been studied, surgical landmarks of the Eustachian tube have not been
previously described or quantified via cadaveric dissection.
The ET was cannulated bilaterally in 5 cadaveric heads with a flexible guide wire
from its middle ear orifice along its course within the middle fossa to its nasopharyngeal
orifice. A zero degree endoscope (Storz, Germany) was used to visualize the wire endonasally
and through its entry into the middle ear orifice via the external auditory canal.
An exoscope (Storz, Germany) was used to visualize as we drilled (Depuy-Synthes) to
expose the length of the Eustachian tube as it extends from the middle ear, along
the course of the middle fossa (lateral to the petrous carotid), and as it transitions
from the horizontal to vertical segment as it leads to the nasopharynx. We defined
this transition point from horizontal to vertical segment, the ET genu.
We divided the ET measurements into three sections: the total ET length (tET) from
nasopharyngeal orifice to the anterior tympanic membrane ridge (just lateral to the
middle ear ET orifice); the anterior segment from the nasopharyngeal orifice to the
genu (aET), and the posterior ET length (pET) along the petrous carotid from the genu
to the anterior TM ridge. Direct measurements of tET and pET were made, while aET
was then calculated.
The mean tET length was 47.6 mm (SD ± 3.1 mm), mean pET length was 24.8 mm (SD ± 4.5
mm), and mean aET length was 21.9 mm (SD ± 5.5 mm); see.
This is the first report to summarize these studies and redefine ET anatomy, specifically
the genu and its position along the length of the organ. This serves the purposes
of current techniques of ET obliteration such as cauterization, packing, and for ongoing
development of a catheter based repair of CSF leak either from an anterior endonasal
approach or a lateral technique. Packing techniques might utilize the entire length
of the ET, while cauterization-based techniques might best avoid the pET lying near
to the petrous carotid. Indeed, prior studies may have underestimated these distances,
as the curvilinear shape of the ET is frequently poorly accounted for. The definition
of the anatomic landmarks and correlation to distance and critical structures provide
the basis for minimally invasive instrumentation/techniques to treat CSF rhinorrhea
from a lateral skull base source.
