Imaging of the sella
In this video from Dr. Katie Bailey, we go through imaging of the sella, including a brief review of the contents of the sella, common pathologies on MRI, and an algorithm for refining your differential diagnosis based on location.
Normal sellar anatomy. The pituitary gland sits in the sella and in general should measure less than 1 cm. The posterior pituitary is intrinsically T1 bright. The gland and infundibulum enhance on postcontrast images. Sometimes the pituitary can appear more convex if the carotid arteries and cavernous sinuses are more medial than expected, which is a normal variant
Empty sella. When the sella is expanded and filled with CSF, this is called an empty sella. Sometimes you can see a thinned pituitary at the bottom or it may be completely compressed. This is most commonly seen in the setting of intracranial hypertension.
Pituitary cysts. These are relatively common lesions, often hypointense on T1 and hyperintense on T2 and do not enhance. Rathke cleft cysts can be T1 hyperintense if they have proteinaceous content. Pars intermedia cysts and Ratke cleft cysts are terms that refer to the same pathologic diagnosis but some people use them differently based on the size/location of the lesions. Adenomas can also have cystic degeneration, particularly if they have been treated.
Pituitary adenomas. These are hypoenhancing lesions which enhance less and more slowly than the adjacent gland. They may fill in with time. Microadenomas are by definition less than 1 cm. The infundibulum will often be deflected away from the pathology because of mass effect.
Macroadenomas. These are pituitary tumors that are greater than 1 cm and may have a snowman appearance with mass effect on the adjacent optic chiasm. These will often involve the cavernous sinuses. Involvement greater than 270 degrees around the carotid is highly suggestive of cavernous sinus invasion, and classification systems such as the Knosp classification can help you be more exact about cavernous sinus involvement.
Other lesions. Other common lesions in the pituitary are metastases, apoplexy (hemorrhage most commonly into a pre-existing adenoma), and meningiomas.
Autoimmune hypophysitis. This is a special type of inflammation of the sella most commonly occurring in patients getting immunotherapy for metastatic melanoma (ipilimumab). The pituitary and infundibulum are commonly diffusely enlarged and enhancing.
Lymphocytic hypophysitis is an inflammatory disease of the infundibulum which may involve the gland itself, but often spares it.
Metastatic disease. Metastases can occur in the pituitary gland or infundibulum. If you see an irregular mass filling the sella in a patient with known malignancy, consider metastases.
Other lesions. Aneurysms of the internal carotid artery, epidermoids, chondrosarcomas, and other vascular variants can all involve the sellar region and infundibulum, so it is important to keep those in mind.
Hopefully you learned a bit from this video about approaching sellar lesions. Be sure to check out the other videos on search patterns as well as all the other
Emergency Imaging of Brain Tumors
This playlist covers the imaging of brain tumors in an emergency setting, with particular emphasis on how a general radiologist might approach these cases and how to formulate a smart differential on CT.
This video is an overview from Dr. Katie Bailey about fractures of the face, including their CT findings and complications. Facial fractures are among the most commonly encountered emergencies, particularly in busy trauma hospitals.
Simple fractures. These involve isolated fractures of one of the sinus walls, the zygomatic arch, or the nasal bones.
Frontal sinus fractures. Consider whether they involve the outer table, inner table, or both. Complications of frontal sinus fractures include CSF leak, mucocele, or meningitis. Brain parenchymal contusions can also accompany frontal sinus fractures.
Other common isolated fractures. Common fractures include the zygomatic arch and mandible. When you have a fracture of the mandible, it is very common to have a fracture elsewhere in the mandibular ring. Nasal fractures are commonly seen and are worse if there is displacement because they can result in poor cosmetic outcomes. Nasal septal fractures are sometimes challenging to see and soft tissue swelling is probably your best clue. A nasal septal hematoma, if present, can result in necrosis of the nasal septum.
Lamina papyracea fractures. These are fractures of the medial wall of the orbit. Most commonly, these result from a blow to the eye. Soft tissue swelling within the orbit or blood in the sinus can tell you if you are likely dealing with a more acute fracture. A retroorbital hematoma can accompany these fractures, and are characterized by stranding or soft tissue density in the retroorbital fat. These require more rapid intervention to avoid risks to vision
Orbital floor fractures. These can have displacement of fragments into the adjacent maxillary sinus, and it is important to report if the muscles are displaced into the sinus. Entrapment of the muscle can result in loss of eye movement and may need to be managed surgically.
Single sinus fractures. Sometimes you will have a fracture of only a single sinus, often from a direct blow. These can involve one or more walls of the sinus. Sphenoid sinus fractures can be complicated by extension into the carotid canal which increases the risk of vascular injury.
Lefort fractures. Lefort fractures involve the pterygoid plates and are subdivided into 3 types. They can be unilateral or bilateral. Lefort I fractures extend through the inferior maxilla and not the roof of the sinus. This is a transverse pattern which is low across the maxillary sinus. Lefort 2 fracture extend through the inferior lateral maxilla but extend superiorly as they go medially through the midface and inferior orbital wall. A Lefort III fracture is a transvere fracture which is higher and goes through the lateral orbital wall and potentially the zygoma.
ZMC fractures. These are fractures of the zygomaticomaxillary complex. They involve the struts of the zygoma, including the anterior maxillary wall, posterior maxillary wall, zygoma, and frontal sinus.
NOE fractures. Nasal-orbital ethmoidal fractures are a pattern of injury etending from the nasal bones through the septum, ethmoid sinuses, and medial orbital walls across the bridge of the nose. These can cause injury to the nasolacrimal duct or medial canthus, reducing eye movement.
Hopefully you learned a bit from this video about how to categorize facial fractures on CT. Be sure to check out the other videos on search patterns as well as all the other head and neck topics.
How to read a Sinus CT
In this video, Dr. Katie Bailey gives us an overview of how to approach a CT of the sinuses, including an overview of anatomy, some common pathology, and red flags to look out for as you interpret the images.
Overview of sinus anatomy. There are 4 main sinuses, the maxillary, ethmoid, sphenoid, and frontal, which are both paired. The nasal cavity and orbits are also important structures to discuss.
Maxillary sinus. When evaluating the maxillary sinus, you should describe whether there is opacification, the appearance of the bony walls, and the outflow tract (the ostiomeatal complex).
Frontal sinus. The paired frontal sinuses should also be described in terms of aeration and bony walls. They drain through the frontoethmoid recess into the anterior ethmoid air cells.
Ethmoid air cells. There are anterior and posterior ethmoid air cells which can have mucosal thickening or opacification. The Haller cell is an important variant in which an ethmoid cell is found below the medial orbit that can contribute to obstruction. Ethmoid sinusitis can extend into the orbits and cause orbital cellulitis, an important complication.
Sphenoid sinus. The sphenoid sinus is posterior to the ethmoids and may have a fluid level, as it is a dependent sinus. The drainage is into the posterior ethmoids via the sphenoethmoid recess. Adjacent structures including the sella, internal carotid artery, and clivus can all be affected by sphenoid sinus disease.
Nasal cavity. Important features of the nasal cavity are the nasal septum, turbinates, and any potential polyps. An important variant is the concha bullosa, which is an aerated middle turbinate, which can contribute to sinus outflow obstruction.
Anatomic variants. Important anatomic variants can affect the optic canal, such as absence of the bone. The olfactory fossa can also have variants where the depth is greater or less. Keros is a classification used to describe how deep the olfactory fossa is. The vidian canal contains the vidian nerve and is best seen on the coronal images just above the pterygoid plates. It can be medially directed and run in the wall of the sphenoid sinus, which exposes it to injury. The carotid canal can be medially positioned and very close to the sphenoid sinus, also putting it at risk of injury. There are variants in the sphenoid septa, in which it attaches along one lateral wall rather than in the midline.
Red flags of sinus imaging. Abnormal soft tissue or stranding in the retromaxillary fat or pterygopalatine fossa is an important red flag which can signal invasive (possibly fungal) sinusitis. Similarly, stranding in the orbit can raise the possibility of invasive sinusitis. Another red flag is bony disruption, particularly along the sinus walls or in the nasal cavity.
Conclusion. Don’t forget to look at other things in the images, including the brain, sella, nasopharynx, mandible, teeth, orbits, and more.
Thanks for checking out this quick video on the internal auditory canal. Be sure to check out the additional videos on other
head and neck topics.
Imaging findings in Pulsatile Tinnitus
In this video, Dr. Katie Bailey talks about the imaging findings of pulsatile tinnitus. Pulsatile tinnitus is a ringing or abnormal sound sensation in the ear, but unlike the most common high frequency tinnitus, it has a pulsatile or wavelike quality that can often oscillate with arterial or venous flow. Causes of pulsatile tinnitus are unique and a different approach is warranted.
General approach and common causes. Some findings are best seen on CT and others are best seen on MRI. For this reason, you can often perform either a CT or MRI when you begin. There are a wide range of possible causes that can be categorized into neoplasm, arterial, and venous.
Paragangliomas. Glomus tympanicum, or tympanicum paraganglioma, is the most common middle ear tumor. These are more common in women than men. The most common location is along the floor of the middle ear adjacent to the cochlea. A glomus tympanicojugulare has features of both a jugular paraganglioma and tympanic paraganglioma, often connecting them. On MRI, these appear as permeative masses with bone destruction and enhancement.
Vestibular schwannoma is the most common tumor of the internal auditory canal and usually arise from the inferior vestibular nerve. These are solidly enhancing masses that extend from the IAC into the cerebellopontine angle.
Other tumors that can occur in or around the region include meningiomas and chondrosarcomas. Meningiomas are usually homogeneously enhancing and may have dural tails. Chondrosarcomas are often centered around the petroclival junction.
Arterial anomalies can also cause pulsatile tinnitus. If the internal carotid artery extends into the middle ear with no bony covering, this is an aberrant ICA. A persistent stapedial artery can also cause pulsatile tinnitus. The absence of foramen spinosum suggests a variant with no middle meningeal artery and a persistent stapedial artery.
Other vascular causes include vascular loops and microvascular compression of the nerves in the IAC. These can also cause pulsatile tinnitus, although the role of an AICA loop has been controversial. Other carotid abnormalities such as carotid stenosis, dissection, or fibromuscular dysplasia are also associated with tinnitus.Hemangiomas, or encapsulated venous vascular malformations, are benign vascular malformations which have high flow
Venous abnormalities can also cause tinnitus. These may be a more constant tinnitus or hum with less arterial type pulsation. Absence of the bony wall around the jugular bulb is known as a dehiscent jugular bulb. Venous diverticula from the sigmoid sinus or jugular vein are small outpouchings of the vein, almost like aneurysms. Other vascular malformations such as dural AV fistulas and arteriovenous malformations can cause tinnitus, and can be confirmed on vascular imaging studies. Idiopathic intracranial hypertension causes stenosis of the lateral transverse sinuses which can also cause tinnitus.
A few other things can cause pulsatile tinnitus, such as cotospongiosis/otosclerosis and Paget disease.
Overall, a number of things can cause pulsatile tinnitus, but a few of these things are more common so you should keep your eye out for them.
Thanks for checking out this quick video on the internal auditory canal. Be sure to check out the additional videos on other
Imaging the internal auditory canals
In this video, Dr. Katie Bailey describes the internal auditory canal including the anatomy and some of the common pathology that you may encounter.
Review of internal auditory canal (IAC) anatomy. The IAC includes arteries and nerves. The most easily seen structures are the facial (cranial nerve VII) and vestibulocochlear (cranial nerve VIII) nerves. On a sagittal view, the anterior portion of the canal contains the facial nerve (superior) and cochlear nerve (inferior). This can be remembered by the mnemonic “7up, Coke down”. The oropharynx includes the tonsils (both lingual and palatine), the squamous mucosa of the pharynx, the uvula, and the vallecula. oral cavity includes the lips, teeth, hard and soft palate, gingiva, retromolar trigone, the buccal mucosa, and anterior 2/3 of the tongue. Masticator space. Contains the muscles of mastication, the mandible, branches of the trigeminal nerve, lymph nodes, and minor salivary glands.
Vascular loop. Sometimes an arterial branch can compress the nerves as they enter the IAC. If you see mass effect, this is particularly possible. Smaller loops of the anterior inferior cerebellar artery are more controversial but has been previously described as associated with hemifacial spasm. If you see it, you can be descriptive about which portion of the nerve is involved.
Vascular malformations are a rare cause of symptoms, but if you see an unusual tangle or cluster of vessels in the region you should
Vestibular schwannomas are the most common tumor affecting the IAC. They usually arise from the inferior vestibular nerve, and have previously been referred to as “acoustic neuromas”. With these tumors, you will see an enhancing mass with pretty homogeneous enhancement centered in the IAC with extension into the porus acousticus. They can sometimes be quite small but still symptomatic.
Meningiomas are the second most common solid mass. They are also solid enhancing masses near the IAC. Key clues that they are not schwannomas are a center outside of the IAC. Dural tails, or linear areas of tumor tracking along the dura, can be helpful, but schwannomas can also have them.
Epidermoids are relatively uncommon non-enhancing masses of the CP angle and IAC. They look cystic on T2 and can be close to CSF, but their key distinguishing feature is hyperintensity on DWI.
Bell’s Palsy is an idiopathic facial paralysis on one side. Imaging can often be normal, but if you see linear enhancement in the distal auditory canal this can be a sign of Bell’s palsy. The geniculate and mastoid portions of the facial nerve can enhance in normal cases, so in those cases you must consider the symmetry.
Red flags in the IAC include nodular enhancement and multiple cranial nerves enhancing. This should make you think of unusual pathology such as lymphoma, sarcoidosis, metastatic disease, perineural spread of tumor, and Lyme disease.
Thanks for checking out this quick video on the internal auditory canal. Be sure to check out the additional videos on other head and neck topics.
How to read imaging of the orbits: a pathology based approach
In this video, Dr. Katie Bailey describes her approach to imaging of the orbit with a focus on common diseases that can affect the orbits. We’ll save neoplasms for another video and focus on other pathologies here.
Review of the anatomy of the orbits. The orbits are surrounded by orbital walls and contain the globes, extraocular muscles, nerves including the optic nerve, a variety of vessels and nerves, and the lacrimal gland.
The globes. Common pathologies involving the globes include ocular lens surgery/removal, retinal detachment and vitreous hemorrhage, and phthisis bulbi (a chronically shrunken and deformed injured globe). MRI is even better at seeing these pathologies and can see tumors within the globe, such as ocular melanoma.
The orbital walls. The most common pathology of the orbital walls are fractures, commonly of the medial or inferior orbital wall. Other common pathologies include invasion of sinusitis into the orbit or carcinoma invading the orbit.
Extraocular muscles. Thyroid orbitopathy often causes symmetric enlargement of the extraocular muscles. IgG related disease and lymphoma can also infiltrate the extraocular muscles. Of these, lymphoma and metastatic disease tend to be more masslike and well defined.
Optic nerve, disc, and sheath. The most common pathology is optic neuritis, which affects the nerve itself. This is common in demyelinating disease. Perineuritis is when the enhancement/inflammation is around the nerve and has a different differential diagnosis. Idiopathic intracranial hypertension (IIH) can cause distended and tortuous optic nerve sheaths as well as elevation of the optic disc (papilledema).
Vessels. The ophthalmic artery is the most visible vein and often can have aneurysms. The superior ophthalmic vein is the largest vessel, and can have varices or thrombosis (often in the setting of infection).
Retroorbital fat. The fat is important because it can be a sign that other structures are abnormal. This is most commonly abnormal in orbital cellulitis, but can also be abnormal if there is a hematoma or orbital inflammatory disease.
Thanks for checking out this quick video on orbital imaging and common non-neoplastic pathology. Be sure to check out the additional videos on other head and neck topics.