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Clinical case: Malignancy along facial nerve: want to learn more about it?

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Clinical case: Malignancy along facial nerve

After reviewing this case you should be able to describe the following:

  • The course and functions of the facial nerve. The signs and symptoms that the patient would likely be showing after the surgery due to the removal of peripheral branches of this nerve. How these signs and symptoms are compared with Bell palsy.
  • The course and function of the vestibulocochlear nerve. The signs and symptoms the patient would likely be showing after removing the peripheral parts of this nerve.
  • The neural contents of the jugular foramen. Why dysphagia developed in this patient postoperatively (jugular foramen syndrome).

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

It has been modified and reviewed by Joel A. Vilensky PhD, Carlos A. Suárez-Quian PhD, Aykut Üren, MD.

Case description

Patient history

A 43-year-old male with type 1 neurofibromatosis (NF1) was seen because of a growing subcutaneous tumor of the right postauricular region.
The tumor had been partially resected previously and had been shown histologically to be a malignant peripheral nerve sheath tumor (MPNST) (Figure 1) which presumably developed from a benign neurofibromatosis tumor. The patient did not have right facial nerve paralysis or hearing impairment.

Figure 1. Histological section from the tumor showing a mitotic cell in a high power field, indicative of a malignancy and consistent with an MPNST (H&E stain, 600X).

Imaging

MRI demonstrated remaining periauricular subcutaneous lesions that appeared to extend medially from the stylomastoid foramen into the intratemporal canal, facial nerve canal to the internal auditory canal (Figure 2).

Figure 2. Preoperative T2 (A) and T1 (B) weighted axial MR scans (without contrast) showing the postauricular MPNST (white circles), which was related to the peripheral part of the facial nerve.

MRI with contrast also showed subcutaneous lesions from the enlarged stylomastoid foramen and also an enlarged facial canal (Figure 3).

Figure 3. All sections are axial T1 weighted MRI images (with contrast) through the petrous portion of the temporal bone. A is the lowest section, followed by B, with C being the highest section. The blue ovals show an enhancing mass that was presumed to be residual MPNST with presumed medial internal spread encompassing the mastoid (blue arrow in A), tympanic (blue arrow in B) and meatal (blue arrows in C) portions of the facial nerve.

Diagnosis and management

Based on these findings, the patient was strongly suspected of having an MPNST that had spread internally along the facial nerve to the internal auditory canal. CyberKnife stereotactic radiosurgery was undertaken with a single dose of 23Gy to the right internal auditory canal.

Subsequently, the surgeons performed a subtotal temporal bone resection, which involved removal of much of the temporal bone including the petrous portion; with this extirpation, the cranial nerves Ⅶ and were cut and the jugular foramen was opened so that some of the higher numbered cranial nerves could be preserved.

Evolution

As a result, the patient suffered a total deficit of functions associated with cranial nerves Ⅶ and Ⅷ as well as incomplete palsy of cranial nerves IX and X (dysphagia). After rehabilitation and surgical treatment with laryngeal elevation and cricopharyngeal myotomy, he gradually resumed eating. Although postoperative adjuvant therapy was not delivered, there was no recurrence at follow-up 24 months after surgery. 

Surgical and anatomical considerations

Origins of malignant peripheral nerve sheath tumors

MPNSTs are rare, aggressive malignant spindle cell tumors that have a poor prognosis, and they may arise from neurofibromas, especially in NF 1 patients as in this case, or directly from normal peripheral nerves. The absence of facial nerve signs and symptoms at presentation was surprising; apparently, despite the tumor’s presence along the nerve, impulse transmission somehow remained unaffected.

Figure 4. Cadaver photograph showing the three (of five) branches of the facial nerve emanating from the superior, anterior and inferior borders of the parotid gland.

Differentiating between neurofibromas and malignant peripheral nerve sheath tumors

In clinical settings, it is important to differentiate MPNSTs from neurofibromas; usually, a neurofibroma precedes the onset of an MPNST particularly in patients with NF 1 (although only a small portion of NF tumors become malignant). Biopsy remains the gold standard for accurately differentiating between NF tumors and MPNSTs.

A biopsy of soft tissue tumors such as in the extratemporal region in this case can be performed relatively easily. In contrast, it is difficult to perform a biopsy of an intraosseous tumor because the considerable destruction of bone is required and, in addition to the effects of this destruction, there is an increased risk of dissemination of malignant tumor cells than if the tumor was left undisturbed. Therefore, MRI features such as larger tumor size, peripheral enhancement, perilesional edema, and intratumoral cystic change are useful in distinguishing MPNSTs from neurofibromas, with these characteristics being more consistent with malignant tumors than benign ones.

Figure 5. A. Histological section of facial canal with facial nerve (H&E, 20X). B. Increased magnification of nerve segment within A (600X) showing that there is no evidence of mitotic cells, suggesting that the tumor was a neurofibroma rather than an MPNST (thus, the internal tumor was likely an independent mass).

In the case described here, there were initially two distinct NF1 tumors; the external one became an MPNST whereas the internal one remained benign. However, the surgeons could not ascertain this with certainly prior to the surgery. Further, even if the surgeons knew that the internal tumor was simply another neurofibroma, there still was at risk of it eventually becoming malignant and thus they may have proceeded with the same surgery anyway. 

Anatomy of the temporal bone

The temporal bone consists of four parts (Figure 6): the squamous, mastoid, petrous and tympanic parts. 

Figure 6. Inferior basal skull view showing some of the features evident in Figure 7, and some of the parts of the temporal bone (see text). In this skull, the styloid process has been broken off, which is common in preserved skulls.
  • The squamous part provides part of the lateral surface of the skull and is the most superiorly positioned component of the temporal bone. The zygomatic process is an anterior projecting process that originates from the squamosal part and articulates with the temporal process of the zygomatic bone. The arched bony bridge formed by the two processes complete the zygomatic arch, which encompasses the temporalis muscle
  • Posteroinferior to the squamosal part of the bone is the mastoid part, consisting of the mastoid process and contained air cells. This process serves as an attachment for the sternocleidomastoid muscles and the air cells communicate with the middle ear (tympanic) cavity via the mastoid antrum. 
  • The petrous part of the temporal bone is situated in the skull base between the sphenoid and occipital bones. This part of the bone is pyramidal in shape and within it lays the middle and internal ear cavities.
  • The tympanic part of the temporal bone is relatively small and lies inferior to the squamous part, anterior to the mastoid part, and superior to the styloid process. The lateral border of the tympanic part gives attachment to the cartilaginous part of the external acoustic meatus. Its anteroinferior surface forms the posterior boundary of the mandibular fossa. The styloid, from the Greek stylos, is a thin bony projection that is inferiorly and anteromedially between the parotid gland and internal jugular vein. The process serves as an attachment for the stylohyoid, styloglossus and stylopharyngeus muscles.
Figure 7. Thin section axial CT of temporal bone showing tumor excavation of facial canal (evident as an enlarged canal). A: tumor osteoclastic destruction of some of the petrous portion of the temporal bone (blue circle). B: mastoid portion (blue circle). C: tympanic portion (blue circle).

Clinical case: Malignancy along facial nerve: want to learn more about it?

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