Introduction and clinical case
En-bloc clearance of malignant deep lobe parotid tumours involving the
stylomandibular tunnel and parapharyngeal space is challenging in view
of the limited surgical access and the critical structures that are
located in close proximity (1). As most of the tumours that involve the
deep lobe of the parotid gland and the post-styloid parapharyngeal space
are benign, they can be removed through blunt dissection with
subcapsular dissection technique (2-3). However malignant tumours
involving this space require clearance with adequate oncological margin;
therefore a good exposure of the surrounding structures is paramount, to
avoid adverse complications during resection.
The technique that we describe is a combined
transmandibular-transmastoid approach that allows complete en-bloc
resection of the deep parotid lobe and stylomandibular tunnel with a
lateral temporal bone resection and a marginal mandibulectomy. This
approach provides good exposure of the critical structures and allows
for an en-bloc resection and good oncological margins.
A 75-year-old female patient had a history of cutaneous squamous cell
carcinoma in the right lower neck with metastases to the right parotid
gland and cervical nodes, undergoing wide excision of the skin lesion,
parotidectomy, selective neck dissection and an anterolateral thigh free
flap reconstruction fourteen months previously. Four months ago, she
presented with a recurrent lesion in the right parotid bed. The contrast
enhanced CT head and neck of the patient shows a heterogeneously
enhancing area involving the right superficial and deep lobes of the
parotid gland with extension through the stylomandibular tunnel into the
parapharyngeal space (figure 1). A complete resection would involve a
total parotidectomy, segmental mandibulectomy, masticator space
clearance and a lateral temporal bone resection with sacrifice of the
involved pinna and facial nerve. The technique described below is an
approach for similar tumours that allows total en-bloc resection with
adequate oncologic margin, in order to maximize the tumour control.
The initial part of the surgery involved a radical parotidectomy
approach. The area of skin involved is shown with a dashed line, while
the final skin margin is shown with a solid line (figure 2). An
extension along the neck was made for completion neck dissection and
exposing the neck vessels for the free flap reconstruction. A
subplatysmal flap/parotid fascial plane was raised radially with
exposure of the entire parotid gland with all the distal branches of the
facial nerve delineated for subsequent facial nerve reanimation. The
junction of the proximal and middle thirds of the body of the mandible
was also exposed to allow an osteotomy as shown.
Next, the lateral temporal bone resection was performed; this involved
an initial cortical mastoidectomy with identification of the antrum,
lateral canal and incus. Using these landmarks, the mastoid portion of
the facial nerve trunk was identified and exposed. The descending
portion of facial was transacted with a section sent for frozen section.
The distal portion of the remainder of the intra-temporal facial nerve
was marked and left in continuity with the rest of the tumour specimen.
A posterior tympanotomy was performed, the incudostapedial joint was
identified and disarticulated. After removal of the incus, malleus head
and division of the tensor tympani, a bone cut was made superiorly along
the zygomatic arch to the superior aspect of the TMJ capsule. Another
bone cut was made inferiorly, anterior to the facial canal, and superior
to the jugular bulb to completely free up the external ear canal.
The facial nerve was then lifted out of the temporal facial canal, with
removal of the mastoid tip and freeing of the soft tissue just deep to
it. The right external auditory canal was then down-fractured, with
en-bloc removal along with the posterior segment of the zygomatic arch
and condyle of the mandible.
Finally, before removal of the entire specimen, the mandible osteotomy
was retracted to expose the medial pterygoid muscle. The muscle was
resected, maintaining a good margin of uninvolved tissue. At this point,
the tumour was freed circumferentially with good margins. The tumour was
then distracted outwards for adequate resection of the deep margin
(figure 3). The final defect is seen in figure 4.
A primary facial nerve reanimation was performed, with a right brow
lift, a lateral canthoplasty, nasolabial lift and cable graft from the
proximal facial nerve stump to the midface branches. A chimeric
anterolateral thigh flap was used, with skin to reconstruct the skin
defect and vastus lateralis muscle to obliterate the mastoid cavity,
after plugging of the eustachian tube opening.
The final tumour margins were circumferentially clear, with a deep
margin clearance of 10 mm. (figure 5). The post-operative period was
uneventful except for a small area of superficial skin loss over the
previous flap. In view of the large volume recurrent disease she was
administered adjuvant radiotherapy, which she completed four months ago.
She is currently disease free. In addition to this case, we have
successfully performed this procedure in other patients (n=4). It can be
reliably repeated in these tumours in a safe manner to achieve adequate
oncological clearance.