Discussion:
Many groups have reported on the vascular flow of the auricle. (3-6)
Blood supply depends on two branches of the external carotid arteries:
1) the superficial temporal artery; and 2) the posterior auricular
artery. These branches form the dense arterial network perforating the
cartilage. Recently, Zilinsky re-evaluated the arterial supply of the
auricle. Superior and inferior auricular branches of the superficial
temporal artery mainly supply the helical rim of the auricle.(6) The
upper third of the helical rim was also supplied from non-performing
branches of the posterior auricular artery. The perforators of the
posterior auricular artery supply the concha, inferior crus, triangular
fossa antihelix, and the ear lobe.(6) Venous drainage occurs through the
accompanying veins of each artery.
LTBR and STBR are popular surgical methods for en bloc resection of
temporal bone malignancy. It is clear that arterial supply to the
auricle is significantly impaired when en bloc resection combined with
parotidectomy is performed or when the superficial temporal artery is
sacrificed. The frequency of auricular complication has not been
elucidated. To our knowledge, Carpenter al. first reported ear
complications in temporal bone surgery.(2) They followed 32 patients who
underwent lateral skull base surgery, including parotid surgery,
subtemporal fossa surgery, and temporal bone surgery. Postoperative
necrosis was found in 3 of the 32 cases. However, that study reported no
statistically significant risk of avascular necrosis when comparing
preauricular and postauricular approaches, suggesting that no detailed
study had previously identified a significant relationship with surgical
procedures.
Simple LTBR can logically preserve the arterial supply of the auricle,
and theoretically preserve anterior venous drainage of the superficial
temporal vein. However, with STBR or LTBR, along with additional
procedures, including parotidectomy and manipulation of the TMJ, it is
impossible to preserve the main arterial branches to the auricle and
both the main anterior and posterior venous drainage routes. We examined
34 cases who had undergone these procedures, and three of them showed
postoperative vascular insufficiency in the auricle. However,
sacrificing main arterial flow did not lead to ischemic auricular
necrosis in any cases. Generally, the facial region has an abundant
arterial network. The result of our study suggests the auricles had
sufficient blood supply via the anastomosis connecting the facial
arterial network. In our study, only one case showed postoperative
auricular necrosis after auricular congestion, due to insufficient
bloodletting after surgery. Appropriate postoperative bloodletting
recovered auricular congestion and preserved the auricle cosmetically in
the other two cases with postoperative vascular insufficiency in the
auricle. These facts imply that venous drainage is crucial for
preserving the auricle after temporal bone resection.
Veins in the face, which include the superior ophthalmic and facial
veins, contain valves that determine blood flow direction.(7, 8) Zhang
et al. mentioned that blood flow in the face is (1) caudal toward the
internal jugular vein in the inferior part of the facial vein; (ii)
normally toward the cavernous sinus in the superior ophthalmic vein; and
(iii) into either the facial vein or the superior ophthalmic vein from
the angular vein.(8) If the two main drainage routes from the auricle
are sacrificed after temporal bone resection, the venous network in the
face may be important for maintaining venous flow from the auricle.
Hosokawa et al. recommend parotidectomy when the tumour invades the
anterior–inferior wall of the canal.(9) If an early-stage tumour
invaded this wall, we applied partial resection of the parotid gland and
soft tissue abutting the canal. Furthermore, total parotidectomy is
recommended for advanced T3 and T4 cases.(10, 11) The superficial
temporal artery emerges from the superior border of the parotid gland
and courses superolaterally between the TMJ and the tragus, and
cross-superficially to the zygomatic process accompanied by the
superficial temporal vein. Therefore, dissecting the
infra-/pre-auricular region and manipulating the TMJ results in
sacrificing the anterior drainage route from the auricular to the
superficial temporal vein. To elevate the auricle, the posterior
drainage route to the posterior auricular vein needs to be divided in
all temporal bone resection cases. During neck dissection, common facial
veins are often ligated. These cause a dramatic change in the venous
flow related to the auricle. Unlike with arterial flow, it is likely
that the valves in veins make it difficult for the venous drainage
system to adapt to changes in blood flow after temporal bone resection.
When pre-/infra-auricular lymphadenopathy is found preoperatively, the
tissue around the lymph node needs to be sufficiently dissected to
achieve adequate surgical margins. Therefore, temporal bone resection
combined with total, superficial, or partial parotidectomy or with TMJ
manipulation leads to sacrificing the main venous drainage from the
auricle to the superficial temporal vein and the posterior auricular
vein. In addition, careful dissection of the subcutaneous tissue around
the lymphadenopathy potentially damages the venous network in the
subcutaneous layer, which can worsen auricular congestion
postoperatively.
Our analysis showed that cases with pre-/infra-auricular lymph node
dissection had a statistically significant risk of auricular
complication in the temporal bone resection (Fig. 5). Neck dissection,
parotid gland resection TMJ manipulation and history of radiation
therapy can worsen the venous drainage, theoretically. In addition, our
study suggest that pre-/infra-auricular lymph node dissection had most
impact to the worsens venous drainage leading to auricular congestion. A
clear consensus on the guidelines for treating external ear congestion
is lacking. Tissue milking, pin pricking,(12) use of medical
leeches,(13, 14) mechanical leeching, (15) and chemical leeching(16) are
the current treatment methods for venous congestion. In our two cases,
mechanical bloodletting effectively salvaged the auricular necrosis.
When the colour of the auricle changes during surgery, either 1)
arterial spasm or 2) venous flow obstruction could be the cause. If
ischemia due to artery spasm is observed, bleeding from the wound is
confirmed after some time. If congestion is observed, it is important to
check whether congestion can be recovered by pinprick, bloodletting and
so on. Sufficient bloodletting should be initiated as soon as possible
following confirmation of auricular congestion by the surgeon.
Our study involved several limitations, including small sample size and
its retrospective nature. In addition, our sample was comprised of only
63 patients. Further studies are needed to confirm the cause and risk
factors associated with auricular complications.