Transcription
Dear colleagues,
This is the second part of Imaging of the petrous B. In the first part, we finished the anatomy, and in the second part, we will deal with the pathology. You remember that we have divided the ear into three parts: the external ear, the middle ear, and the inner ear. The same will be followed considering the pathology. We will handle the abnormalities in the external ear, then the abnormalities of the middle ear, then we will finish by the abnormalities of the inner ear.
One of the well-known anomalies of the external ear is the atresia of the external canal. We have two types of external canal atresia: the membranous type or the soft tissue type, and the bony type. We remember that the external canal is filled normally with air, which is continuous through the external meatus with the exterior, and it terminates by the tympanic membrane, which is fixed to the tympanic annulus. You may find some soft tissue densities within the external canal representing ear wax, and this is the normal appearance in the coronal plane of the external canal with its bony part and the cartilaginous part, ending by the tympanic membrane, which is most likely at this particular site. You will see the famous part of the bone which is known as the scutum. We mentioned it in the anatomy and we will repeat something about it in the pathology.
Look at this example. You can see that the external canal is small. It is totally obliterated by soft tissue density, and there is no air inside the canal connecting it to the exterior. Also, this is a coronal image. In many of these cases, you can find some deformities of the ear pinna, what's known as microtia.
Then, in this example, you can see that the right external canal is good and is filled with air. The bony part, the cartilaginous part, ending by the site of the tympanic membrane, and this is the scutum. On the left side, you cannot see any canal. There is bone immediately subcutaneous, and there is no canal similar to the previously seen in the previous case. This is what we call the bony atresia of the external canal.
It is important to assess the integrity of the middle ear as well as the inner ear structures in cases of external canal atresia, whether the soft tissue atresia or the bony atresia. In this example, the right canal is good, and the ossicles are also of normal size and configuration. While on the right side, you can see bony atresia of the external canal, and the middle ear cavity is relatively smaller compared to the right one. The ice cream cone is no more an ice cream cone, but you can see deformed and almost fused ossicles on the left side.
This is the coronal image. On the right side, you can see normal appearance of the external canal, while on the left side, you cannot see the external canal, and you see the bony mass formed by the ossicles. In many cases, you can see that the ossicles are also fused to the arthritic plate or the inner aspect of the middle ear cavity.
One of the famous inflammatory processes affecting the external auditory canal is known as necrotizing otitis externa, and was previously known as malignant otitis externa. This term is no more preferred in clinical practice in order not to mix with malignant tumors, for example. Then we may say that this is an aggressive infection, necrotizing otitis externa, and this aggressive infection is usually caused by *Pseudomonas* and is frequently seen in all diabetic patients.
Then you can see that the external auditory canal is there, but it is filled by enhancing granulation tissue. In the bone window, you can see erosion of the walls of the external auditory canal with extension of the granulation tissue into the middle ear cavity. In the parapharyngeal area, you can see that there is also inflammatory granulation tissue involving the pterygoid muscles, involving the wall of the nasopharynx, and extending into the infratemporal fossa. It is also seen spreading into the region of the temporomandibular joint.
On the right side, the one-window image at a higher level showed that the middle ear cavity is also involved by inflammatory material with bone erosions. But the ossicles are more or less intact. On the left side, you can see that the middle ear cavity is obliterated by soft tissue density. The ossicles are more or less intact, and this is just otitis media.
This is another example of necrotizing otitis externa, previously known as malignant otitis externa, and you can see the involvement here is on the left side. The external auditory canal is filled by enhancing inflammatory granulation tissue compared to the normal right-sided external auditory canal. Also, you can see the inflammation is involving the region around the temporomandibular joint with erosions of the mandibular head, and also involvement of the muscles of mastication, together with infiltration of the retropharyngeal soft tissue structures. In the bone window image, you can see some erosive changes of the skull base bones.
Here are two different examples for lesions that can occur near the ear or involving the petrous bone. This is just an osteoma or ivory osteoma, which has been discussed in detail in the sector of bone tumors. It is an osteoma with no medullary cavity that is frequently seen in the flat bones and usually encountered in the paranasal sinuses as well.
This is the classic example of fibrous dysplasia affecting the petrous bone on the left side, and you know that fibrous dysplasia is diagnosed by bone expansion and the ground glass configuration of the affected bone. What's important here is the effect of fibrous dysplasia on the middle ear cavity as well as on the inner ear structures.
This is just the bilateral, almost symmetrical narrowing of the external canal due to osteomas or exostoses of the bony margins of the external canal, which is bilateral and almost symmetric. This is usually caused by contact with cold water and seen mostly in swimmers and surfers. Then, if you see this appearance, it is almost diagnostic and is usually seen on both sides and is almost symmetric.
Then, as any bone in the body is prone for metastatic deposits, and this is a destructive lesion involving the left mastoid in a patient known to have a bronchogenic carcinoma, representing metastatic deposit from the lung cancer. This is an aggressive lesion, a large soft tissue component obliterating the external canal, bulging the skin contour, and also infiltrating the subcutaneous tissues with aggressive bone destruction of most of the petrous bone, including the external canal and the middle ear cavity as well. In the coronal images, you can see the extent of bone destruction is involving most of the petrous bone, except for some of the inner ear structures as well as the internal canal. You can also see the destruction of the middle ear cavity, and these are the ossicles, the erosion of the tegmen tympani. This has been pathologically proved to be squamous cell carcinoma of the external canal.
This is a particular or a peculiar example of a lesion which is considered by many as a spot diagnosis. This is the histiocytosis of the petrous bone or Langerhans cell histiocytosis, where you can see this frequent appearance of bilateral, almost soft tissue masses centered to the region of the external auditory canal. You know that this disease is of unknown etiology, and it can affect many bones all over the body, and external and middle ear involvement are common, as high as 61%. The bony labyrinth is resistant to erosion by this histiocytosis, and involvement of the inner ear is considered rare.
Then, at many cases, you can see these soft tissue masses centered to the region of the petrous bone associated with bony erosive changes. If you look carefully, you can see that there are other lesions affecting the lateral orbital wall on both sides, the greater wing of the sphenoid here, in the squamous part of the temporal bone. If you look also at any sites in the body, you can see similar lesions.
Then, histiocytosis is diagnosed usually by the presence of bilateral, almost symmetrical involvement of the base of the petrous bone, centered to the external canal. This bilateral involvement is considered diagnostic of histiocytosis, and it's easy to have a biopsy from these lesions because they are prominent and immediately subcutaneous.
Then, if you are asking about the differential diagnosis, you know that otitis media is not associated with such bone destruction and extra soft tissue component. Rhabdomyosarcoma is usually unilateral, not bilateral, and the diagnosis of metastasis requires that you know that the patient had a non-primary malignancy.
Then we came to infection of the middle ear. Here you can see some fluid inside the middle ear cavity. You appreciate the integrity of the ice cream cone in the middle ear cleft. It's easy to see these fluid opacifying the mastoid antrum as well as most of the air cells. Then you know that the infection is usually dependent. When you turn the patient's position from supine to prone, there will be a change in the relation between air and the fluid. In the supine position, fluid will be in the dependent part. In the prone position, the fluid will also be in the dependent part.
Here you look for the opacification of the middle ear cavity, mastoid air cells. You look for the integrity of the ossicles, and of course, you need the clinical support of otitis media in order to be sure that you are dealing with an inflammatory process. You know that the inflammatory granulation tissue inside the middle ear cavity in cases of otitis media and also in cases of cholesteatoma does not show any contrast enhancement in CT or MRI. Then the discrimination between otitis media and cholesteatoma does not depend on the appearance after contrast injection. Both do not enhance, and you depend mainly on the presence of some air within the middle ear cavity to look for the dependency of the fluid. Then you are dealing with otitis media. If the lesion is non-dependent, then you think immediately of a cholesteatoma. Also, if the middle ear cavity is totally opaque, such as in this case, and you cannot judge the dependency of the fluid, then you need very much the help of the clinical data because the clinician is able to differentiate between otitis media and cholesteatoma just by looking through the otoscope.
This is a lesion which affects the apex of the petrous bone and is considered as a rare complication of otitis media and mastoiditis. This lesion is also caused by *Pseudomonas*, and this infection extends through the Dorel canal. This canal contains the cranial nerves V and VI. Then we got some nerve palsies along the distribution of both nerves in the CT scan, and you can see some bone erosions and rarefaction in the affected apex of the petrous bone. Usually, you do not see enhancement in the affected area, but minimal enhancement can be appreciated.
Here you see this is a lesion in the apex of the petrous bone on the right side, and you can see the fluid within the middle ear cavity and the mastoid. In this T2 image, noting the presence of media and mastoiditis associated with apical petrositis, you know that this is an enhancement or around the apex of the petrous bone. Then you can see here, this is an example of apical petrositis on the right side. If you look carefully, this is the normal apex of the petrous bone, and here you can see there is some increased signal compared to this area in this T2 weighted image. You also see the fluid signal within the mastoid. In this post-contrast T1 weighted image, you see that this is the normal fat in the skull base bones, and this is the normal appearance of the apex of the petrous bone on the left side. Here you can see there is some enhancement of the apex of the petrous bone together with the inflammation in the mastoid air cells.
The differential diagnosis of apical petrositis may include epidermoid cysts or cholesterol granuloma, which is frequently seen at this site but has a different appearance. Metastatic deposits, which usually need a known history of primary malignancy for accurate diagnosis. Also, eosinophilic granuloma, we have mentioned it has a specific appearance. Chordoma and meningioma have also specific CT and MRI appearances which are almost different from this apical petrositis.
Then, this is what we call cholesterol granuloma, which is also a lesion occurring at the apex of the petrous bone, but it is totally different from apical petrositis. In this lesion, you can see an expanding osteolytic lesion involving the apex of the petrous bone on the left side. This lesion is usually containing cholesterol, meaning that it will show some hypodensity on the CT scan due to the presence of fat, and it will show hyperintense signal in both T1 and T2 weighted images. This is the bone window showing the expanding lesion involving the apex of the petrous bone, and this is the soft tissue window showing the hypodensity of the lesion. This is another example showing the lesion at the apex of the left petrous bone with evident high signal intensity in this T1 weighted image. In the T2 weighted image, you can see some drop of the signal intensity, and in the T1 fat-suppressed image, you usually do not see suppression of the cholesterol within this cholesterol cyst or cholesterol granuloma. This is another example of cholesterol granuloma at the apex of the petrous bone, and this is T1, T1 post-contrast, and T2 weighted image showing the high signal intensity, and you do not appreciate any enhancement in the lesion after contrast injection.
Then we came to the issue of cholesteatoma, and we have two types: the congenital type and the acquired type. Congenital cholesteatoma is a cholesteatoma which is not preceded by a history of middle ear infection. Then you see in all cases of cholesteatoma, whether congenital or acquired, a soft tissue density within the middle ear cavity which is not dependent; it does not change its position by the change in the patient's position. Many ENT surgeons know the diagnosis of cholesteatoma by just looking through the otoscope, and you can see a glistening lesion behind the drum, which is intact in cases of congenital cholesteatoma and may be perforated in cases of acquired cholesteatoma.
This is a good example of a cholesteatoma in the middle ear cavity near the two dots which represent the handle of the malleus and the longer process of the incus, and it is non-dependent, denoting that it represents a cholesteatoma. Here is the otoscope appearance of this cholesteatoma. Here you can see a soft tissue density which is hanging within the middle ear cavity behind the ossicles, and you know that cholesteatoma, whether congenital or acquired, do not show any contrast enhancement. This is the appearance of the cholesteatoma posterior to the ossicles. This is also a male child, 4 years old, with cholesteatoma on the left side. You see a soft tissue mass which is not dependent. It is seen medial to the ossicles, which are more or less intact, and you can also appreciate the integrity of the eardrum as well as the clear appearance of the external auditory canal.
Acquired cholesteatoma has two types: the attic cholesteatoma, which is very common, and the sinus cholesteatoma, which is relatively uncommon. Acquired cholesteatoma is a sequela or one of the complications of otitis media. This is the way by which the cholesteatoma will form inside the middle ear cavity. First, you get some infection within the middle ear, then you get some retraction of the eardrum with protrusion of the epithelium inside the middle cavity, which is entrapped and started to grow. This will form a mass that will frequently destroy the ossicles. One can appreciate that this mass starts near the scutum, which is a very small bone that will be eroded first by the cholesteatoma. This was considered a sign of cholesteatoma in the era before CT and MRI. Whenever you look to the hypocycloidal tomography and you see that the scutum is eroded, then you know that the lesion in the middle ear cavity will represent a cholesteatoma.
Then here you see this acquired cholesteatoma, and it's a non-dependent lesion which is located in the middle ear cavity. This is the rim of the eardrum, and you can see the erosive changes in the surrounding bone. Also, remember this is the site of the scutum, and you can appreciate this on the normal side. This is the scutum, and this is the eardrum, and these are the ossicles. The diagnosis of cholesteatoma depends on the presence of a non-dependent, non-enhancing lesion associated with some erosive changes of the surrounding bones. Ossicles are eroded in 30% of attic cholesteatoma and in 10% of sinus cholesteatoma.
If you look carefully here and see that the middle ear cavity is expanded, the inner wall is markedly irregular and eroded, there is subtotal destruction of the ossicles, and you may feel that there is some erosion of the lateral semicircular canal. This erosion will result in communication between the inner ear and the middle ear, and this is known as labyrinthine fistula.
Then here is another example of cholesteatoma secondary to chronic otitis media on the right side. You can see that the middle ear cavity is almost totally obliterated by soft tissue density, and you do not see the ossicles in all these images, meaning that they are totally eroded. But you can see that the tegmen tympani is more or less intact, and this is cholesteatoma on the right side. This is also a non-dependent mass which is seen in the upper part of the middle ear cavity, and you see the irregularity of the inner margin of the middle ear cavity. If you look carefully, this is the cochlea, and there are two dots above the cochlea, and these two dots represent the segments of the facial nerve canal. This is the tympanic segment and this is the labyrinthine segment. Here you can see that cholesteatoma has eroded the tympanic segment, and this will result in affection of the facial nerve, leading to facial palsy.
If there is erosion of one of the semicircular canals, which is frequently the lateral one because the lateral semicircular canal is the nearest canal to the middle ear cavity, then you get what is known as labyrinthine fistula, which means that there is a communication between the inner ear and the middle ear. Then erosion of the tegmen tympani will result in extension of the infection into the cranial cavity, and this may lead to meningitis or dural abscess or dural sinus thrombosis.
This is a good example of cholesteatoma in the middle ear cavity. The ossicles are no more seen; they are totally destroyed. There are areas of rarefaction of the tegmen tympani, and this is the vestibule, this is the lateral semicircular canal, which is eroded, and this is the cochlea and the internal canal. Then you are dealing with a case of labyrinthine fistula secondary to cholesteatoma.
This is an example of cholesteatoma with the erosion and destruction of the tegmen tympani and consequent extension of the infection into the brain, leading to the formation of a cerebral abscess in the temporal lobe, which is marginally enhancing, surrounded by extensive, very focal brain edema. This is the same case by MRI. You see fluid signal within the mastoid and the middle ear cavity, and you can appreciate the marginally enhancing lesion in the temporal lobe representing an abscess. Of course, you know that these are effects from the blood flow.
This is a lesion which is considered the most common primary neoplasm of the middle ear. This is the glomus tympanicum, one of the glomus tumors that are frequently seen in the head and neck, and this is one of the common locations inside the middle ear cavity. The diagnosis is clinically easy by looking through the otoscope, and you can see a vascular red lesion behind the drum. Then the need for imaging is to confirm the diagnosis and also to see the extension of the lesion inside the middle ear.
Here you see a non-dependent lesion in the middle ear cavity, which is indistinguishable from cholesteatoma, but based on the clinical settings and also based on contrast enhancement, you can diagnose glomus tympanicum. You remember cholesteatoma does not show any contrast enhancement, but glomus tympanicum of course will enhance. Then if you see a lesion like this in the CT scan and you want to differentiate between glomus and cholesteatoma, then you need to inject contrast media, but you can use the clinical data if they are available, and the clinical data will support your diagnosis.
Then this is an example of a lesion on the left side. This lesion is a soft tissue mass within on the right side, I'm sorry, in the middle ear cavity, and in the T2 image, it shows some brightness, and in the post-contrast image, it shows enhancement. This is the confirmatory test because you know that cholesteatoma does not enhance, and if the lesion is enhancing like this, and you know that this is a vascular lesion, it will represent glomus tympanicum.
This is another example by CT and MRI. T1 weighted image after contrast injection, a non-dependent lesion is seen within the middle ear cavity. You remember these structures: the sinus tympani and the facial recess, and after injection of contrast, you can easily appreciate the enhancement of the lesion, diagnostic of glomus tympanicum. This is also an example by CT, and the clinical setting supports the diagnosis of glomus tympanicum.
Then we came to fractures of the petrous bone, and we have two types: the longitudinal fracture, which involves the long axis of the petrous bone, and the transverse fracture, which is across the axis of the petrous bone. Longitudinal fractures are very common compared to transverse fractures, and these fractures usually affect the middle ear structures, leading to conductive hearing loss. Sequelae of trauma may result in otorrhea or hemorrhage inside the tympanic cavity, conductive or sensorineural hearing loss depending on the part of the ear to be involved, vertigo, and facial nerve palsy if the facial nerve canal is involved, CSF leakage, and meningitis. These are the complications.
In this particular example, you can see that there is a longitudinal fracture passing through the longitudinal course or the longitudinal axis of the petrous bone, and it involves the middle ear cavity. Here you can see this is part of the ice cream cone, which is the ice cream, and you don't see the cone here, which is most likely displaced. This means that there is complete disruption of the incudomalleal joint.
This is the transverse fracture, which is relatively uncommon compared to the longitudinal fracture. It affects the petrous bone perpendicular to its long axis, and this fracture frequently involves the inner ear and will result in sensorineural hearing loss. Here you can see this fracture affects the superior semicircular canal. It also passes through the vestibule. This is the lateral semicircular canal, and this is the vestibule. Then the transverse fractures are uncommon, and they affect the inner ear structures.
These are some of the complications of fractures, starting by the presence of blood inside the middle ear cavity and mastoid antrum after trauma. If you see fluid within the middle ear cavity, this is hemorrhage. You remember that this is the vestibule, and in the vestibule, you can see some air, and this is known as pneumolabyrinth, the presence of air inside the inner ear structures. Also, in this example, you see that the ice cream is relatively away from the cone, and this means that there is subluxation of the incudomalleal joint.
This is the normal appearance of the ice cream cone in this ear. You can see the ice cream, and you don't see the cone. There is complete disruption of the incudomalleal joint with dislocation of the incus. It may be somewhere in the middle ear cavity. Here are two different examples of longitudinal fractures. In this example, you see fluid within the middle ear cavity representing hemotympanum, and you can appreciate the disruption of the incudomalleal joint with evident subluxation or even dislocation of the joint itself. In this example, you see hemotympanum also, and you see subluxation of the incudomalleal joint. This is an example of dislocation of the incudomalleal joint. This is the ice cream, and this is the cone. This is the head of the malleus, and this is the body and the short process of the incus, surrounded by blood in the mastoid antrum.
Then we came to the inner ear structures, starting by this abnormality, which is one of the well-known abnormalities. It's known as large endolymphatic duct and sac, or it may be called vestibular aqueduct syndrome. You remember that the vestibular aqueduct is the duct which is seen in the axial images posterior to the posterior semicircular canal. This is the vestibule, this is the lateral semicircular canal, and these two dots represent part of the posterior semicircular canal. The width of the vestibular aqueduct does not exceed 1.5 mm, but in this example, you see that the vestibular aqueduct is very wide. This is the vestibule, and this is the posterior semicircular canal. The vestibular aqueduct is very dilated, and this is known as vestibular aqueduct syndrome or large endolymphatic duct and sac, which is considered a common cause of sensorineural hearing loss.
By MRI, it's easy to see the endolymphatic duct and sac. This is the CT, and this is the MRI. Here is the vestibule, lateral semicircular canal, the two dots represent the posterior semicircular canal, and this is the vestibular aqueduct and the sac, which are filled with endolymph. You can appreciate this structure as high signal in the MRI T2 weighted image. By vestibular aqueduct syndrome, you see marked widening of the vestibular aqueduct on the right side and also marked widening of the vestibular aqueduct on the left side.
Actually, there are two types of inner ear dysplasia: the first one is the Michel anomaly, and the second one, which is relatively more common, known as Mondini anomaly. Michel anomaly means total absence of the inner ear structures. Then if you look here by these CT scans, you can see the middle ear structures, but you cannot see any of the inner ear structures. This may be better appreciated by MRI, especially in the T2 weighted images, because you know that the inner ear is seen by virtue of the high signal fluid, endolymph, inside the inner ear structures. But here you cannot see; you cannot appreciate any high signal structures representing the inner ear on both sides. Then you know that there is total aplasia of the inner ear structures, and this is known as Michel anomaly.
You know that in some patients, we can proceed with cochlear implantation in order to improve hearing, especially whenever there is a cause of sensorineural hearing loss. But you should remember that in order to perform the operation of cochlear implant, you should have a normal, well-formed cochlea. You cannot perform the cochlear implant in absence or in cases of malformed cochlea. The cochlea should be intact so that you can introduce this electrode, as you can see here, which is connected to the external structure, and this electrode is pushed as deep as they can into the turns of the cochlea.
This is the X-ray performed after bilateral cochlear implant in order to ensure the position of the electrode inside the cochlea, and this is the CT scan showing the same issue. This is the electrode which is pushed through the round window into the basal turn of the cochlea, then pushed up to the one and a half turns of the cochlea until it reaches the dome or the superior turn of the cochlea, as you can see in these CT images.
What about Mondini malformation? Mondini means that the inner ear structures are present, but they are deformed; they are of abnormal configuration. This is the normal appearance. You remember the vestibule, the lateral semicircular canal, the posterior semicircular canal, and this is the vestibular aqueduct. This is the internal canal, and this is the dome of the cochlea, and this is the middle ear structures and the ice cream cone. If you look here, you can see that the cochlea, as well as the vestibule and some of the semicircular canals, have been transformed into a single cavity of abnormal configuration. This appearance is diagnostic of Mondini anomaly, whether it is unilateral or bilateral.
Then this is the normal configuration of the vestibule, lateral semicircular canal, and the dome of the cochlea. But here you see that the vestibule and the lateral semicircular canal form a single cavity, and the dome of the cochlea is markedly dilated, as you can see here. This is also diagnostic of Mondini anomaly, bilateral Mondini anomaly affecting the dome of the cochlea, the lateral semicircular canal, and the vestibule. They are of abnormal configuration. You can also easily diagnose this abnormality by MRI, where the inner ear structures are no more showing the normal configuration; they are transformed into a cavity which may be unilocular or multilocular.
Also, in the course of Mondini anomaly, you can see the vestibular aqueduct syndrome as well. In this example, this is the basal turn of the cochlea, one and a half turns of the cochlea, and this is the dome of the cochlea. They are more or less towards the normal configuration, but the vestibule here is very wide, the lateral semicircular canal is short, and you can see that the vestibular aqueduct is considerably dilated.
Sometimes you get normal widening of the internal auditory canal without the presence of intracanalicular tumors, and this is known as mega internal auditory canal. It's also filled by CSF, and there is no abnormality inside the canal or in the cerebellopontine angle. This is the normal canal, and this is the mega internal auditory canal. Mega internal auditory canal means that the internal canal is abnormally wide, but it contains CSF, and the nerves are going through the canal undisturbed. This is the diagnosis of mega internal auditory canal.
But if the canal contains a soft tissue mass, and the diagnosis is acoustic neuroma, which is the most common intracanalicular and cerebellopontine angle enhancing lesion. This is a good example by MRI showing an intermediate signal lesion within the internal canal in T1-weighted image, and after contrast enhancement, it shows homogeneous contrast enhancement with some extracanalicular component. This is also another example, T2 image of an intracanalicular acoustic neuroma, and T1 post-contrast showing the intra and extracanalicular components. This is a sizable acoustic neuroma at the cerebellopontine angle with intracanalicular component and a component in the cerebellopontine angle showing heterogeneous post-contrast enhancement.
Here, remember that I have discussed these issues in detail in the lecture of the posterior fossa imaging in the series of brain imaging.
Otosclerosis means that there is obliteration of the oval window by a bony plate. Normally, you see the oval window in the coronal images connecting the middle ear cavity to the vestibule. It is occupied by the footplate of the stapes, as you know. But in this example, you can see that the oval window is no more present and is totally obliterated by a bony plate, diagnostic of otosclerosis.
Then we have another disease with the presence of bone inside the labyrinth, and this is known as labyrinthine ossification. In this example, you see that there is bone in the dome of the cochlea on the right side compared to that on the left side. Labyrinthine ossification means that you have bone inside the labyrinth, which means the vestibule, semicircular canals, and the cochlea. This is the normal appearance: this is the vestibule, lateral semicircular canal, posterior semicircular canal, and dome of the cochlea. But here you see soft tissue density within the middle ear cavity, which may be due to otitis media. If you look here, you cannot see the lateral semicircular canal and you cannot see the vestibule, and you can see the shadow of the dome of the cochlea. They are totally ossified.
Labyrinthitis ossificans is one of the common causes of deafness in childhood, and this is the sequela of suppurative infection of the labyrinth, which is one of the complications of meningitis. In some cases, whenever there is meningitis, there may be a chance for the organism to reach the inner ear structures, resulting in suppurative labyrinthitis, which may end by ossifying sensorineural hearing loss. After an attack of meningitis, then you can detect labyrinthitis ossificans as early as two months following this meningitis. Severe ossification of the labyrinth may preclude the possibility for cochlear implantation.
This is an example in normal condition: you see the vestibule, the lateral semicircular canal, the posterior semicircular canal, the vestibular aqueduct. But in cases of labyrinthitis ossificans, you see total ossification of the superior semicircular canal. Here is the one and a half turns of the cochlea, which are normal. In this case, you see bone within one and a half turns of the cochlea, and this is a case which presented by profound sensorineural hearing loss following an attack of meningitis. You remember that meningitis is one of the common causes to result in labyrinthitis ossificans secondary to suppurative labyrinthitis.
Then this syndrome is an important syndrome which is known as the superior semicircular canal dehiscence syndrome. If you look here and see this is the superior semicircular canal, and this canal is separated from the brain by a bony plate. In this syndrome, this bony plate is absent, and the canal is in direct contact with the dura. This is an example here. You see this is the superior semicircular canal, which should be protected by bone at this side to separate it from the brain, but in this dehiscence syndrome, you can see that the superior semicircular canal is dehiscent. There is no bone separating it from the brain. This is the normal appearance: the superior semicircular canal separated by bone from the brain, and this is the syndrome where you see the superior semicircular canal is not separated by bone from the brain.
Now, what does this syndrome mean? This syndrome means that the sound waves come to the external canal, affect the eardrum, and affect the ossicles, which will transmit the sound waves to the oval window, and then the oval window will transmit the sound to the fluid in the vestibule, and then to the cochlea, which will be decompressed at the round window at the end of the cochlea. That is to say, there should not be any sound waves going through the semicircular canals. But if there is dehiscence here, and this is considered a third window. You know we have two windows: the oval window and the round window at the end of the cochlea. But if there is a third window created by the dehiscence of the superior semicircular canal, this will allow sound waves to be transmitted through the semicircular canals, and this will be interpreted by the brain as the patient moves. This way will result in some dizziness for the patient if he is exposed to loud sounds, if he has this superior semicircular canal dehiscent syndrome.
This is the sagittal image which is reconstructed in an oblique fashion along the course of the superior semicircular canal, and you see that this part of the canal is dehiscent, it is directly in contact with the dura.
Then we came to facial neuritis, or what's known as Bell's palsy. This is a clinical diagnosis; it needs no imaging. But if you perform imaging, you can see that this is the canal of the facial nerve. You remember the ascending limb, the geniculate ganglion, and the descending limb. Normally, if you inject contrast media, the nerve does not enhance, but in cases of Bell's palsy, the nerve will enhance, but it will show normal caliber. We usually need imaging, and this imaging should be performed, of course, with contrast enhancement. It's better performed by MRI rather than CT scan in cases of resistant or lesion which does not respond to treatment and is progressive on follow-up, suggestive of the presence of neoplasm, for example.
In the coronal images, you need; you can see these are the two segments of the facial nerve canal in the CT scan above the cochlea, and then in the coronal T1 weighted image after contrast enhancement, you can see the enhancing segments of the facial nerve, denoting the presence of facial neuritis. You need imaging in cases of unresolving or progressive course of the lesion, as I have mentioned. Facial nerve schwannoma is uncommon, and it is usually seen in the region of the geniculate ganglion or may affect the ascending or descending limb of the facial nerve canal.
If you look here, this is the normal appearance of the facial nerve canal: ascending limb, geniculate ganglion, and descending limb. In this particular region, you can see a soft tissue mass which is indistinguishable from cholesteatoma, for example. But if you inject contrast, the facial neuroma will show contrast enhancement. This is the axial image, and this is the coronal image. You remember this is the cochlea, and you have two dots above the cochlea representing the segments of the facial nerve. These segments are no more seen, and they are replaced by a soft tissue mass here, which is most likely representing a facial schwannoma. If you inject contrast media by MRI, better of course. This is the axial image by CT, and this is the axial T1 weighted image by MRI, and you can see the enhancement, diagnostic of facial nerve schwannoma.
This is also an example. In normal cases, you see the cochlea with two dots above representing the segments of the facial nerve canal. But in these two dots are not seen here; they are replaced by a soft tissue mass, which represents the facial schwannoma. You know that the facial nerve also goes inside the internal auditory canal, and neuroma can arise from the facial nerve inside the internal auditory canal. But in such cases, you can never discriminate between acoustic neuroma and facial schwannoma because facial neuroma inside the internal auditory canal will result in sensorineural hearing loss, exactly similar to acoustic neuroma. Also, consider that acoustic neuroma is by far more common than facial schwannoma inside the internal canal. Then you can appreciate the facial schwannoma if it occurred along the course of the facial nerve here, and you see it. This is part of the facial nerve inside the canal, but this is the clue for the diagnosis: the lesion or the enhancement is extending along the ascending limb of the facial nerve canal, diagnostic of facial schwannoma.
Finally, in some conditions, you have to assess the patient for cochlear nerve atrophy. This assessment can be performed if you have the sagittal T2 weighted images for the internal canal. Normally, inside the internal auditory canal in the sagittal image, you see four nerves. Two nerves are adjacent to each other, and these are the superior and inferior vestibular nerves. This nerve will represent the facial, and the lower one will represent the cochlear nerve. Then in cases of cochlear nerve atrophy, whether it is secondary to vascular abnormality, inflammatory, or trauma, you will see three out of four nerves. The two closely related nerves represent the vestibular components: the superior and inferior vestibular nerves. The upper one is the facial, and the lower one is missing, and this is diagnostic of sensorineural hearing loss.
Thank you very much. Alhamdulillah.