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Perineural Spread of Tumor Along the Fifth and Seventh Cranial Nerves
Updated: Jun 16, 2006
Introduction
Perineural spread of a tumor, or spread along a nerve, is one of the more insidious forms of tumor growth. Facial, skin, sinus, nasopharyngeal, and salivary gland tumors have a propensity to spread along this pathway. Most of these are malignant tumors, such as squamous cell carcinoma (SCCa), adenocystic carcinoma (ACC), lymphoma, and metastatic tumor. Other rarer malignant tumors, such as rhabdomyosarcoma, can also spread along these pathways in the suprahyoid head and neck region. Benign tumors, such as schwannoma, neurofibroma, meningioma, hemangioma, and juvenile angiofibroma, may spread along this pathway as well. Prior to antibiotics, infections of the face could spread along this pathway into the brain, resulting in abscesses and empyemas. Once a process has accessed the perineurium, it can spread centrally to distant sites in the cranial vault or, less likely, peripherally to more superficial facial structures.
Clinical manifestations of perineural tumor spread may be subtle or nonspecific, with burning or other dysesthetic sensations, trismus, or in advanced disease, muscle denervation atrophy. Even when marked perineural tumor spread is noted on imaging studies, the patient may have no clinical symptoms. Imaging studies may be the only way to detect perineural tumor spread, and therefore, findings may greatly alter therapeutic planning and prognosis. Because perineural tumor spread involves very small deeply located structures, diagnostic imaging misses may contribute to tumor recurrence because of inadequate total tumor volume treatment or failure to target all involved areas.
In order to understand perineural tumor spread, one must understand the ways that tumors can spread. Malignant neoplasms may spread by eroding through bony or fascial structures into the next adjacent compartment space, but benign tumors and infectious processes are less likely to directly invade bone and fascia. Lesions may also spread from one bony or fascia-lined space into an adjacent one via natural dehiscences in fascia or through foramina, fissures, or canals within bone. This type of spread is along a pathway of least resistance. This is the most likely method of spread for benign tumors and infections and can occur with malignant neoplasms as well.
In other areas of the suprahyoid neck, tumor spread most commonly occurs via lymphatic channels and less commonly via venous structures with eventual emboli to the rest of the body via the arterial structures. Once tumor in the lymphatic system enters the vena cava, tumor can metastasize to the lung and eventually to the rest of the body via the arterial system.
Because lymphatics are usually absent around nerves, perineural spread is guided by other factors. Most think that perineural tumor spread takes place along pathways of least resistance.
After the vagus nerve, the facial and trigeminal nerves are the longest cranial nerves (CNs) and they have the most branches in the suprahyoid neck region. Because of the number of branches and the proximity to most head and neck neoplasms, that these two nerves are the nerves most commonly involved in perineural spread is not surprising. The trigeminal and facial nerves and their branches traverse a complicated system of interconnected tunnels, channels, and tubes. Understanding the complex anatomy of bony structures and fascia-lined spaces that contain the nerves allows an understanding of perineural tumor spread and its imaging characteristics.
The bony structures most important to an understanding of perineural tumor spread are the bones forming the boundaries of the pterygopalatine fossa and the adjoining fascial spaces, which surround the trigeminal nerve branches, and the temporal bone, which surrounds the facial nerve.
This article reviews the normal anatomy of the pterygopalatine fossa, the trigeminal nerve, and the facial nerve so that pathology in these areas may be recognized. Readers are also urged to review anatomy texts as well as the works of Daniels or Curtin regarding the anatomy of the pterygopalatine fossa. All of the possible pathways of tumor spread along CN V and CN VII are discussed. Examples of pathology on CT scanning or MRI are provided.
CT scanning and MRI play complimentary roles in imaging perineural tumor spread. CT scanning shows the bony changes quite well, which is important because a substantial portion of the trigeminal and facial nerves are surrounded by or contained within bony structures. Bony destruction may be inferred from MRI by soft tissue tumor within the expected areas of bony canals or channels. MRI is superior to CT scanning in evaluation of soft tissue tumors and in its ability to discriminate between normal and tumor tissue. MRI is much better in assessing intracranial spread to the Meckel cave, the cavernous sinus, the cisternal portion of the trigeminal nerve, and the facial nerve in the internal auditory canal (IAC) or cerebellopontine angle (CPA).
With both modalities, normal fatty tissue is quite important in detection of perineural tumor spread. On both CT scanning and MRI, fatty replacement by soft tissue tumor is a very important finding. If either study leads to suspicion of perineural spread, the other study should also be performed because the information is usually complementary. This dual imaging approach detects all possible sites of tumor spread.
Although malignant neoplasm is the most common and most serious of the tissue types that can spread in a perineural fashion, remember that benign pathology, such as hemangioma, meningioma, juvenile angiofibroma, infectious processes, and pseudotumor, can also spread by this route. Lesions involving the trigeminal and facial nerves are not necessarily malignant tumors.
Anatomy Of The Pterygopalatine Fossa
The pterygopalatine fossa is a small space just behind the maxillary sinus and in front of the pterygoid plates of the sphenoid bone. The pterygopalatine fossa is closed along its medial margins except at its superior margin where the sphenopalatine foramen is located. The sphenopalatine foramen opens into the nasopharynx, although the foramen is covered by mucosa. Small nerve branches of the maxillary nerve as well as arteries and veins course through this foramen. The lateral margin of the pterygopalatine fossa is the pterygomaxillary fissure (PTMF), which directly communicates with the masticator space. The inferior portion of the pterygopalatine fossa becomes a bony channel or channels, through which various branches of the greater and lesser palatine nerves exit. The inferior-most termination of the pterygopalatine fossa is at the hard palate, where it becomes the foramina for the greater and lesser palatine nerves.
The superior portion of the pterygopalatine fossa communicates directly with the inferior orbital groove and inferior orbital fissure along its anterior margins. Along its posterior margins, the pterygopalatine fossa communicates with the Vidian canal and the foramen rotundum. A small pharyngeal canal communicates with the posterior aspect of the pterygopalatine fossa below the other 2 canals. Unlike the other above-mentioned structures, the pharyngeal canal cannot be visualized by either MRI or CT scanning.
The sphenopalatine foramen is at right angles to the Vidian canal and the foramen rotundum. This is why Curtin referred to the pterygopalatine fossa as the crossroads.
Anatomy Of The Trigeminal Nerve
After it exits from the skull base, the branches of the trigeminal nerve are contained largely within bony structures or fascia-lined spaces.
The first division of the trigeminal nerve, the ophthalmic nerve, exits from the trigeminal ganglion, which is contained within the Meckel cave, and continues forward within the walls of the cavernous sinus. From the walls of the cavernous sinus, the ophthalmic nerve exits through the superior orbital fissure along the roof of the orbit as the supraorbital nerve to exit from a notch along the superior orbital rim to supply sensation to the skin of the forehead.
The second division of the trigeminal nerve, the maxillary nerve, also exits from the Meckel cave to travel within the walls of the cavernous sinus just below the first division. From the cavernous sinus, the maxillary nerve exits the skull base through the foramen rotundum, which courses along the inferior edge of the lateral walls of the sphenoid sinus and joins the pterygopalatine fossa along its posterior margin. The maxillary nerve exits from the foramen rotundum and crosses the pterygopalatine fossa. From the anterior aspect of the fossa, it continues forward along the infraorbital groove as the infraorbital nerve and then enters the infraorbital canal. The infraorbital nerve exits from the infraorbital canal just below the infraorbital rim to supply sensation to the skin of the cheek, lower eyelid, upper lip, and side of the nose.
In the pterygopalatine fossa, the maxillary nerve gives off two pterygopalatine nerves that join the pterygopalatine ganglion (or sphenopalatine ganglion). The ganglion splits into the greater palatine nerve and multiple smaller lesser palatine nerves, which pass through similarly named foramina to reach the edge of the hard palate. The greater nerve supplies the hard palate, and the lesser nerves supply the soft palate, uvula, and tonsil.
Small nasopalatine nerve branches from the pterygopalatine ganglion exit from the medial aspect of the pterygopalatine fossa and enter the nasopharynx mucosa through a mucosa-covered sphenopalatine foramen.
The posterior superior alveolar nerve or nerves leave the maxillary nerve just before it enters the infraorbital groove and courses through the lateral wall of the maxillary sinus.
The third division of the trigeminal nerve or mandibular nerve exits directly from the floor of the Meckel cave through the foramen ovale. It then travels along the medial aspect of the masticator space giving off branches to the masseter, temporalis, medial and lateral pterygoid, tensor veli palatini, and tensor tympani muscles. The mandibular division also gives off the auriculotemporal nerve, which passes through the parotid gland to supply sensation to the temporal scalp, and the lingual nerve, which courses to the tongue to supply sensation. The mandibular division continues as the inferior alveolar nerve and enters the mandibular canal through the mandibular foramen. It continues in the mandibular canal to the mental foramen where branches exit to supply sensation to the skin of the chin and the lower lip.
Anatomy Of The Facial Nerve
After the facial nerve exits from the pons in the CPA, it enters the IAC, located superior and anterior to the vestibulocochlear nerve. From the IAC, the facial nerve courses forward and in a lateral direction through the fallopian canal until it joins the geniculate ganglion, located along the anterior petrosal ridge near the dehiscence for the greater superficial petrosal nerve. From the geniculate ganglion, the facial nerve takes a hairpin turn and extends in a posterior direction to course posteriorly along the medial wall of the middle ear cavity just above the oval window.
At the posterior end of the middle ear cavity, the facial nerve takes another right-angle turn to descend in the vertical facial canal to exit eventually at the stylomastoid foramen at the skull base. From the stylomastoid foramen, the facial nerve descends into and splits the parotid gland along its long axis gland into a deep and superficial portion. All of the major trunks of the facial nerve branch out within the substance of the parotid gland.
Along its course, the facial nerve gives off several branches. The greater superficial petrosal nerve exits from the geniculate ganglion and courses along the floor of the temporal fossa in a groove extending forward below the Meckel cave and lateral to the carotid canal. The sympathetic plexus surrounding the carotid artery gives off a branch, the deep petrosal nerve, which then joins the greater superficial petrosal nerve to form the Vidian nerve, which then enters the Vidian canal. The Vidian canal is located inferior and medial to the foramen rotundum. If the skull base is extensively pneumatized, the Vidian canal may appear as a bony ridge floating up from the floor of the sphenoid sinus. The Vidian nerve terminates at the pterygopalatine (or sphenopalatine) ganglion in the pterygopalatine fossa.
In the middle ear cavity, the facial nerve gives off a small branch to the stapedius muscle, and within the vertical facial canal, the facial nerve gives off another branch, the chorda tympani. The chorda tympani reascends to the middle ear cavity to exit via the petrotympanic fissure, then descends in the masticator space to join the lingual nerve of the third division of the trigeminal nerve.
Despite the numerous superficial branches of the facial nerve to the face, no reports exist to date of facial nerve perineural tumor spread from superficial skin cancers accessing the numerous branches of the muscles of facial expression. Therefore, this article does not discuss the superficial branches distal to the parotid gland.
Communications Between The Nerves
The trigeminal and facial nerves directly communicate in 3 locations. First, the pterygopalatine (or sphenopalatine) ganglion forms a junction between the Vidian nerve and branches of the maxillary nerve. The Vidian nerve origin is from the greater superficial petrosal nerve branch of the facial nerve, and the maxillary nerve is the second division of the trigeminal nerve. Second, the chorda tympani, a branch of the facial nerve, directly joins the lingual nerve, which is a branch of the mandibular nerve or the third division of the trigeminal nerve. Third, the auriculotemporal branch of the mandibular nerve crosses through the body of the parotid gland at right angles to the facial nerve and here usually has direct communications with the facial nerve. These regions where the nerves communicate allow tumor to spread perineurally from one nerve to the other.
Additionally, the bony channels and fissures that surround the branches of the trigeminal nerve communicate and allow spread of neoplasm from one division of the trigeminal nerve to another. Potential communication exists between the first and second divisions of the trigeminal nerve at the orbital apex where they are in close proximity to each other after passing through the superior orbital fissure. The inferior orbital fissure joins the pterygopalatine fossa and allows potential spread of tumor from the ophthalmic nerve in the orbit to the maxillary nerve in the pterygopalatine fossa. The orbit also communicates with the masticator space through the inferior orbital fissure. Thus, a lesion from the ophthalmic nerve or the maxillary nerve may spread directly to the mandibular nerve. The direct lateral communication of the pterygopalatine fossa through the pterygomaxillary fissure to the masticator space allows potential spread of neoplasm between the maxillary and mandibular nerves.
All of these connections are important because they serve as channels for perineural tumor spread. Once tumor has reached the pterygopalatine fossa or the foramen rotundum, it can spread into the cavernous sinus, into the Meckel cave, and eventually along the cisternal portion of the trigeminal ganglion into the lateral aspect of the pons. Likewise, from the pterygopalatine fossa through the Vidian canal, tumor can spread to the petrous bone to involve the facial nerve. Knowledge of these connections allows physicians to predict where tumor may eventually spread. Thus, physicians can systematically review the complicated anatomy of the skull base on imaging studies in a logical fashion to evaluate the extent of tumor.
Tumor Spread Along The Trigeminal Nerve
Superficial forehead SCCa can access the supraorbital nerve of the ophthalmic division of the trigeminal nerve and spread centrally to the superior orbital fissure/orbit apex and then to the inferior orbital fissure, which joins to the pterygopalatine fossa, and retrograde into the foramen rotundum to enter the cavernous sinus. From the pterygopalatine fossa, tumor can access the Vidian canal and thus spread retrograde into the petrosal portion of facial nerve. Likewise, orbital apex lesions, such as metastases, lymphoma, or pseudotumor, can enter the inferior orbital fissure and thus access the PTMF via the pterygopalatine fossa. Superficial cheek or nasal cutaneous SCCa can access the infraorbital nerve and then spread retrograde along the nerve to the pterygopalatine fossa.
SCCa of the maxillary sinus can invade the lateral walls and thus access the superior alveolar nerve and then spread retrograde to the pterygopalatine ganglion in the pterygopalatine fossa. However, SCCa of the maxillary sinus can also invade the posterior wall and thus directly invade the pterygopalatine fossa just behind the maxillary sinus. In addition, tumor from the maxillary sinus can exit via various draining ostia into the nasal cavity and then spread to the nasopharynx. From the nasopharynx, tumor can then enter the pterygopalatine fossa via the sphenopalatine foramen.
The most common access site reported is from nasopharyngeal tumors, of which SCCa is the most common to spread by perineural tumor spread. Tumor accesses the sphenopalatine foramen located posterior to the nasal cavity near the roof of the nasopharynx and close to the sphenoethmoid recess. From the sphenopalatine foramen, tumor accesses the pterygopalatine fossa. Theoretically, oropharyngeal tumor can access the pharyngeal canal, which joins directly to the pterygopalatine fossa. However, to date no reports of perineural tumor spread by this route exist. Oropharyngeal tumors can also spread in the superficial mucosal space to the nasopharynx and again access the pterygopalatine fossa via the sphenopalatine foramen.
Tumors of the masticator space most often are secondary to tumors elsewhere that access the pterygopalatine fossa and then spread in a lateral direction through the PTMF into the masticator space. The most common of these secondary tumor sources would be nasopharyngeal SCCa. However, primary tumors of the muscle, such as rhabdomyosarcoma, lymphoma, and (rarely) metastatic tumor (not a primary tumor of course), can arise within the masticator space.
Orbital tumors can also directly access the masticator space via the inferior orbital fissure. Because the masticator space contains the main portion of the mandibular nerve, which ascends along the medial margins of the masticator space, tumors can ascend to the foramen ovale, then to the Meckel cave, and then along the cisternal portion of the trigeminal ganglion into the lateral aspect of the pons. Tumors of the parotid gland can spread not only in a perineural fashion centrally along the facial nerve, but also via the auriculotemporal nerve to the mandibular nerve, and thus up to the foramen ovale. The most common tumor of the parotid gland to spread in a perineural fashion is adenocystic carcinoma. Other malignant tumors of the parotid, such as acinic cell carcinoma or mucoepidermoid carcinoma, could potentially spread by this pathway, however.
Tumors of the mandible can spread in a perineural fashion along the mandibular nerve up to the foramen ovale. Tumors of the hard and soft palate can access the greater and lesser palatine nerves. From these nerves, tumor can ascend to the pterygopalatine fossa.
Peripheral spread is less common. Lesions that involve the pterygopalatine fossa can spread into the cheek region along the infraorbital groove or into the orbit via the inferior orbital fissure. Tumors arising within the petrous bone involving the facial nerve can spread antegrade along the greater superficial petrosal nerve and then the Vidian nerve to the pterygopalatine fossa and its ganglion. Tumors such as meningioma may involve the cisternal portion of the trigeminal nerve and may spread antegrade into the Meckel cave and then antegrade, either to the pterygopalatine fossa via the Vidian canal or downward through the foramen ovale to the masticator space.
Tumors may exit the pterygopalatine fossa to the cavernous sinus via the foramen rotundum or to the greater superficial petrosal nerve via the Vidian canal. From the cavernous sinus, tumors can spread to the Meckel cave and then along the cisternal portion of the trigeminal nerve to the lateral aspect of the pons or the trigeminal nuclei. From the greater superficial petrosal nerve and geniculate ganglion, tumors can spread either to the IAC/CPA region or into the middle ear cavity and eventually down the vertical facial nerve canal to the stylomastoid foramen. To date, no report exists of antegrade spread down the pharyngeal canal to the oropharynx. If the tumor spreads antegrade from the pterygopalatine fossa, the exit points may be the cheek or the orbit. The exit point for tumor accessing the mandibular nerve is the Meckel cave bypassing the cavernous sinus. From the Meckel cave, tumors can then spread back to the pons.
Depending on the reported series, up to 50% involvement of the facial nerve may be noted when the pterygopalatine fossa is involved by tumor. Again, the 2 most important connections between the trigeminal and facial nerves are the Vidian nerve joining the second division of the trigeminal nerve to the greater superficial petrosal nerve of the facial nerve and the parotid gland joining the third division of the trigeminal nerve to the facial nerve. Another potential communication could be from the facial nerve via the chorda tympani branch of the facial nerve to the lingual nerve, which arises from the third division of the trigeminal nerve. Therefore, if perineural tumor spread involving the trigeminal nerve is noted, carefully examine the facial nerve for signs of tumor spread there as well.
Most nasopharyngeal tumors, if bulky enough, cause eustachian tube dysfunction and benign inflammatory changes within the petrous and mastoid bone. This may be confused with perineural tumor spread into the temporal bone. However, with perineural tumor spread, low signal is observed on the T2-weighted MRI (especially if the tumor type is SCCa) and abnormal contrast enhancement of the tumor is noted, which does not occur with benign inflammatory changes.
Other potential and much smaller communications exist between the trigeminal and facial nerves, as well as other potential access sites at the terminal branches of both nerves. However, perineural tumor spread along these other potential sites has not been reported to date.
Tumor Spread Along The Facial Nerve
The primary access point of tumor to the facial nerve is via the stylomastoid foramen at the base of the skull adjacent to the styloid processes. Thus, the most common tumors to access the facial nerve are SCCas of the external ear/skin or tumors of the parotid gland either SCCa or adenocystic carcinoma. Once in the vertical facial canal, tumor can then ascend to the middle ear cavity and exit either via the eustachian tube down into the oropharynx (very rare) or out from the geniculate ganglion along the greater superficial petrosal nerve, which becomes the Vidian nerve. Thus, tumor accessing the facial nerve could spread to the pterygopalatine fossa along the Vidian nerve and thus the pterygopalatine ganglion of the maxillary nerve.
Tumors can also follow the course of the facial nerve past the geniculate ganglion to the fallopian canal and exit from the IAC into the CPA region and eventually into the cranial nuclei of the facial nerve within the medulla. Very rarely, tumor within the temporal fossa can access the geniculate ganglion through the hiatus along the anterior petrosal ridge from which the greater superficial nerve exits. From the geniculate ganglion, tumor can then access the middle ear cavity and even extend down the vertical portion of the facial canal.
Probably the most common way for tumors to reach the facial nerve is by secondary involvement from a tumor that has accessed the pterygopalatine fossa and spread in a retrograde fashion along the Vidian nerve to the geniculate ganglion of the facial nerve. From the geniculate ganglion, tumors can spread either to the IAC or into the middle ear cavity and down the vertical portion of the facial canal.
Imaging Approach To The Evaluation Of Perineural Tumor Spread
Certain tumor types and certain locations should raise suspicion of perineural tumor spread. SCCa of the nasopharynx, maxillary sinus, or superficial cheek and forehead has the propensity to spread in a perineural fashion involving mainly the trigeminal nerve. Therefore, inspect all possible access and exit points to the pterygopalatine fossa for possible tumor and thus distal tumor spread or metastasis or even an unsuspected primary source of tumor. Tumors in the lateral aspect of the pons should also raise suspicion of perineural tumor spread, with tumors from an extracranial source spreading in a retrograde fashion along the cisternal portion of the trigeminal nerve to its cranial nuclei.
Metastatic and even primary tumors along the lateral pons would be very unlikely. Suspect perineural tumor spread in cases of tumors in the Meckel cave, cavernous sinus, and foramen ovale region. Meningiomas may occur in these regions as well, but another component to meningioma usually is found. It is rarely confined only to the areas mentioned above.
If perineural tumor spread is suspected, carefully examine all components of the pterygopalatine fossa and its adjacent visceral spaces for the presence of tumor. The most important surrounding visceral spaces are the masticator space, the carotid space, and the parotid space. Within the pterygopalatine fossa, fatty tissue dominates on both CT scanning (low signal) and MRI (high signal on T1-weighted images). Abnormality is heralded by replacement of fatty tissue by soft tissue mass, which may enhance. Bony expansion of canals, fissures, or foramina or even frank destruction by soft tissue mass are also CT scan findings of perineural tumor spread. Perineural tumor spread to the mastoid may be confused with benign inflammatory changes that may occur if the eustachian tube is obstructed.
However, inflammatory changes do not usually contrast enhance as a solid mass on MRI, and they also show bright signal on T2-weighted images. On the other hand, perineural tumor spread does show abnormal solid contrast enhancement, and if the primary is an SCCa, the abnormal soft tissue within the temporal bone is of low signal on T2-weighted images.
CT scanning and MRI play complimentary roles. Obviously, CT scanning is better suited for demonstration of bony changes. MRI is far superior in resolving the different types of soft tissues, particularly in separating tumor from normal soft tissue. The ability to scan direct coronal and sagittal planes makes MRI more versatile. CT scanning probably should be the first study of choice because it is less dependent on patient cooperation and patient motion. If questions are raised by the CT scan findings, then MRI should also be performed.
The advent of fat-suppression techniques has rendered tumor detection much easier, especially in detecting abnormal contrast enhancement. Fat due to its proton content is white on T1-weighted MR images and can obscure or hide white due to abnormal contrast enhancement.
Only comparison of the precontrast with the postcontrast MR could effectively demonstrate abnormal enhancement. Fat suppression is done in 2 ways. The older method, often referred to as short tau inversion recovery (STIR), allows fat signal to be suppressed by using an inversion recovery method and scanning the patient when the fat signal has recovered from a negative position and is now at the zero point, before it returns to its maximal original signal. By imaging with this STIR technique, fat becomes dark.
The second method tunes for the resonant frequency of fat and then contantly bombards the body with this resonant frequency, not allowing the fat protons to relax, and, thus, fat signal is absent or dark. This allows the abnormal white areas to be be seen better, which reflects abnormal pathology with contrast extravasation. Despite this advantage, the degree of contrast enhancement varies, but is usually minimal for SCCa.
Spiral CT, with its ability to image 1-mm thin slices and its ability to clearly show bony changes, still makes CT the study of choice compared with MR. At this time, a combination of both studies probably provides maximum evaluation of the patient.
Multimedia
 | Media file 1: Perineural spread of tumor along the fifth and seventh cranial nerves. This pictorial diagram lists the pertinent nerve branches related to the trigeminal nerve and the pterygopalatine fossa, as well as the facial nerve and its relation to the pterygopalatine fossa. |
 | Media file 2: Perineural spread of tumor along the fifth and seventh cranial nerves. This diagram depicts the bony channels that allow communication with the pterygopalatine fossa. |
 | Media file 3: Perineural spread of tumor along the fifth and seventh cranial nerves. This diagram shows that the pterygopalatine fossa is a very small space located posterior to the maxillary sinus and anterior to the pterygoid plates. |
 | Media file 4: Perineural spread of tumor along the fifth and seventh cranial nerves (CNs). This diagram demonstrates the communication of the pterygopalatine fossa with the masticator space through the pterygomaxillary fissure (PTMf) in axial projection as on a CT scan. The relations of the branches of CN V with the adjacent visceral spaces in the face region are also shown. |
 | Media file 5: Perineural spread of tumor along the fifth and seventh cranial nerves. This is an axial CT scan of a patient with biopsy-proven squamous cell carcinoma of the left nasopharynx. The soft tissue tumor within the left sphenopalatine foramen (SPf) is enlarging it as well as enlarging the adjacent pterygopalatine fossa (PPf). |
 | Media file 6: Perineural spread of tumor along the fifth and seventh cranial nerves. This patient has squamous cell carcinoma (SCCa) of the nasopharynx that has accessed the pterygopalatine fossa (PPf) via the sphenopalatine foramen (SPf). The neoplasm has spread to the left masticator space through the pterygopalatine fossa and along the Vidian canal into the left temporal bone to involve the facial nerve. This contrast-enhanced tumor is of low signal on T2-weighted images (not shown), confirming that this is SCCa rather than secondary mastoid inflammatory changes due to obstruction of the eustachian tube. Spread of tumor has also occurred, with destruction of the left half of the clivus. Compare the normal right pterygopalatine fossa, which is a thin space behind the maxillary sinus and is filled with fatty tissue. Note that the entire left temporal fossa exhibits abnormal contrast-enhanced tumor. This is most likely due to tumor accessing the foramen spinosum along with the middle meningeal artery, which is located in its entirety lateral to the foramen ovale. This is not perineural tumor spread, but it does result in involvement of the entire inferior temporal fossa dura. Axial postcontrast T1-weighted image. |
 | Media file 7: Perineural spread of tumor along the fifth and seventh cranial nerves. This is the same patient as in Image 6 but at a higher level of a T1-weighted postcontrast MRI. Tumor has spread from the highest portion of the pterygopalatine fossa into the cavernous sinus on the left side, which is quite enlarged compared to the normal right side. From the cavernous sinus, the tumor has spread along the cisternal portion of the trigeminal ganglion into the lateral pons. This spread along the cisternal portion is true perineural tumor spread, whereas that within the pterygopalatine fossa is also perineural tumor spread but could be a pathway of least resistance in a bony canal. |
 | Media file 8: Perineural spread of tumor along the fifth and seventh cranial nerves (CNs). This depicts the same patient as in Image 6. This is a sagittal T1-weighted postcontrast MRI through the temporal bone showing perineural tumor spread from the nasopharynx to the pterygopalatine fossa and to the Vidian canal. Further spread of tumor is along the horizontal and vertical portions of the facial nerve (CN VII)—the so-called walking cane appearance. In addition, tumor is also present within the left mastoid and temporal bones. |
 | Media file 9: Bilateral nasopharynx squamous cell carcinoma with invasion of the left half of the clivus appears on this axial T1-weighted postcontrast MRI. There is also soft tissue tumor within the bilateral Meckel cave, which normally are of cerebrospinal fluid signal rather than this soft-tissue signal. There is also perineural tumor spread along the right Vidian nerve (short yellow arrows) back to the geniculate ganglion of the petrosal portion of the facial nerve (CN VII). |
 | Media file 10: Perineural spread of tumor along the fifth and seventh cranial nerves (CNs). This is an axial T1-weighted postcontrast MRI of a patient with known squamous cell carcinoma (SCCa) of the right ear which has accessed the right facial nerve (CN VII) via the stylomastoid foramen at the skull base and has spread along the vertical segment of the facial nerve up to the petrous apex and into the middle ear cavity and anterior to the geniculate ganglion with spread beyond the anterior margin of the left petrous ridge to the Vidian nerve. |
Keywords
perineural spread of tumor along the fifth and seventh cranial nerves, perineural tumor spread, head and neck tumors, pterygopalatine fossa, pterygopalatine fissure, squamous cell carcinoma, adenocystic carcinoma, Vidian nerve, auriculotemporal nerve, trigeminal nerve, facial nerve, tumor growth, SCCa, ACC
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Further Reading
Keywords
perineural spread of tumor along the fifth and seventh cranial nerves, perineural tumor spread, head and neck tumors, pterygopalatine fossa, pterygopalatine fissure, squamous cell carcinoma, adenocystic carcinoma, Vidian nerve, auriculotemporal nerve, trigeminal nerve, facial nerve, tumor growth, SCCa, ACC
