1、Home Abdomen Breast Cardiovascular Chest Head Neck Musculoskeletal Pediatrics Neuroradiology Miscellaneous Cases Top Sites Newsletter Sella Turcica and Parasellar Regionby Walter Kucharczyk and Marieke HazewinkelRadiology department of the University of Toronto, Canada and the Radiology department t
2、he Medical Centre Alkmaar, the Netherlands Anatomic Approach to Differential Diagnosis Pituitary Microadenoma Pituitary Macroadenoma Rathke Cleft Cyst Craniopharyngioma Meningioma Aneurysm Aneurysm vs Meningioma Hamartoma Hypothalamic and Chiasm Glioma Germinoma Chordoma Metastases back to overview
3、print Publicationdate:10-8-2008This review is based on a presentation given by Walter Kucharczyka and was adapted for the Radiology Assistant by Marieke Hazewinkel. In this review a systematic anatomic approach to differential diagnosis of a sellar or parasellar mass is described. By clicking on one
4、 of the subjects in the list on the left, you will go directly to this item.If you have printing problems with the margins of the document, you may have to adjust the margins in the page set up of your internet browser, which you will find in the top left of the menu bar.Anatomic Approach to Differe
5、ntial DiagnosisIn order to analyze a sellar or parasellar mass on MRI we use the following anatomic approach: 1. First identify the pituitary gland and sella turcica. 2. Then determine the epicenter of the lesion and whether it is in the sella or above, below or lateral to the sella. 3. If it is in
6、the sella, determine whether or not the sella is enlarged. 4. Once the location of the mass is clear, analyze the signal intensity patterns: is the lesion cystic or solid? 5. Does it contain any abnormal vessels? 6. Are there any calcifications? And so on. 7. Finally establish a Differential Diagnos
7、is. Pituitary gland On a coronal section through the brain the reference structure is the pituitary gland which lies in the sella turcica. It is usually larger in females than in males - in females the superior border tends to be convex, whereas in males it is usually concave. The most common abnorm
8、alities that arise in the pituitary gland are pituitary adenoma, Rathkes cleft cyst and craniopharyngioma. Pituitary stalk The next structure to identify is the pituitary stalk. This is a vertically oriented structure which connects the pituitary gland to the brain. It is thinner at the bottom and t
9、hicker at the top. Embryologically, it is also derived from Rathkes cleft epithelium and therefore the pathologies, which can arise in the pituitary gland can also arise in the stalk. There are a few unusual things to be considered in children, such as germinomas and eosinophilic granulomas. In adul
10、ts metastases and occasionally lymphoma can arise in the pituitary stalk. Optic chiasm Another major structure in the suprasellar cistern is the optic chiasm. It is an extension of the brain and looks like the number 8 lying on its side. It is glial tissue - therefore the most common tumors to origi
11、nate here are gliomas. In the US and Europe another frequent pathology in this region is demyelinating disease - particularly multiple sclerosis. This can also be associated with some swelling of the optic chiasm. Hypothalamus Further cephalad lies the base of the brain, which at this location is th
12、e hypothalamus. Anatomically the hypothalamus forms the lateral walls and floor of the third ventricle. The most common pathologies to arise here are gliomas - in children hamartomas, germinomas and eosinophilic granuloma.Carotid artery A very important structure in this area is the internal carotid
13、 artery. It runs a complex anatomic course as it passes through the skull base shaped like an S on lateral views. It passes through the cavernous sinus. The segment cranial to this is known as the supracavernous segment.This bifurcates into the anterior cerebral artery, which passes cranially to the
14、 optic chiasm, and the middle cerebral artery, which runs laterally. Aneurysms and ectasias are pathologies that can arise here. One must also be aware of congenital variations in the course of the internal carotid Sometimes it is very medially positioned and can actually lie in the midline. Caverno
15、us sinus The cavernous sinus is a paired complex of venous channels.In the lateral wall of the sinus run nerve III (oculomotorius), IV (trochlearis), V1 and V2 (trigeminus). The sixth cranial nerve (abducens) runs more medially and is located caudal to the carotid artery. The most common pathologies
16、 occurring in the cavernous sinus include schwannomas arising from the cranial nerves and inflammation, which can lead to thrombosis.This is known as cavernous sinus thrombophlebitis. Carotid-cavernous fistulas are fistulous communications between the carotid artery and the veins of the cavernous si
17、nus.Meninges The meninges cover the cavernous sinus.They are thicker laterally and superiorly than medially and inferiorly. The most common tumor to arise from the meninges is of course the meningioma. Dural metastasis is the second most common tumor to arise here. Also inflammatory pathologies occu
18、r in the basal meninges - the most common infection being tuberculous meningitis. Of the non-infectious inflammatory pathologies sarcoidosis is the commonest.Sphenoid sinus Inferior to the pituitary gland lies the sphenoid sinus. This structure contains air and is lined by mucosa and bone.Posterior
19、to the sphenoid sinus lies the clivus (not shown on this coronal section through the brain). Pathology that arises in this area includes carcinomas arising from the mucosa of the sphenoid sinus - squamous cell carcinoma and adenoid cystic carcinoma are the most common. Chordomas arise in the clivus
20、and chondrosarcomas and osteosarcomas also occur in this area.Metastases can occur anywhere. Bacterial or fungal inflammatory processes in the sphenoid sinus can spread intracranially via the cavernous sinus. Pituitary MicroadenomaPituitary MicroadenomaBy definition, pituitary microadenomas are less
21、 than 10 mm in diameter and are located in the pituitary gland. These images show a classic case: on T1 a lesion about 3-4 mm in diameter, slightly hypointense compared to normal pituitary tissue, located in the pituitary gland.On T2, the lesion is slightly hyperintense. The differential diagnosis:
22、pituitary microadenoma or Rathkes cleft cyst (the two can be indistinguishable).The sensitivity of an unenhanced MRI scan for detecting pituitary microadenomas is about 70%. It is not always necessary to give intravenous contrast for detecting pituitary microadenomas as patients with a negative scan
23、 generally receive the same symptomatic treatment as patients with a microadenoma (usually these patients are women with symptoms of hyperprolactinemia). The purpose of the scan is to rule out any large lesions. In possible surgical candidates (for example patients with failed medical therapy or pit
24、uitary disease not amenable to medical therapy such as Cushings disease) it is necessary to give contrast to localize the lesion as accurately as possible.On an unenhanced scan, approximately 70% of all pituitary microadenomas can be detected. If you give gadolinium, you can reduce the false-negativ
25、e rate from 30% to 15%. As mentioned earlier, this usually does not affect patient management. Coronal T1 and T2-weighted images and T1-weighted images before and after gadolinium. In this patient the lesion in the pituitary gland is only detectable after the administration of intravenous contrast.
26、The differential diagnosis: pituitary microadenoma or Rathkes cleft cyst. Pituitary MacroadenomaBy definition, pituitary macroadenomas are adenomas over 10mm in size. They tend to be soft, solid lesions, often with areas of necrosis or hemorrhage as they get bigger. As they grow, they first expand t
27、he sella turcica and then grow upwards. In this example of a pituitary macroadenoma there is suprasellar extension with elevation and compression of the optic chiasm. Because they are soft tumors, they usually indent at the diaphragma sellae, giving them a snowman configuration. This is one feature
28、that can help distinguish between a pituitary macroadenoma and a meningioma. Another feature which can help differentiate them is enlargement of the sella turcica - this generally only occurs with pituitary macroadenomas that originate in the sella. On the left another example of a pituitary macroad
29、enoma. The lesion starts in the sella, which is enlarged, and extends into the suprasellar cistern. Note the classic snowman configuration caused by constriction by the diaphragma sellae. Notice the blood-fluid level, indicating hemorrhage. The usefulness of observing the inclination of the diaphrag
30、matic leaflets was referred to earlier. On the T2-weighted images on the right you can see that the leaflets are displaced upwards by this macroadenoma which started in the sella and is growing upwards. A lesion originating above the sella and growing downwards would push the leaflets in the other d
31、irection (this can be seen with meningiomas for example). Usually the diagnosis of a macroadenoma is straightforward.Sometimes a meningioma can give a similar appearance.On the left an example of a meningioma. Note there is no diaphragmatic constriction and there is uniform enhancement after the adm
32、inistration of intravenous gadolinium which is typical of meningioma. These images are of a transsphenoidal resection of a pituitary macroadenoma. After the bony floor of the sella turcica has been removed, the dura is incised with a cruciate incision. Because the pressure above the dura is larger t
33、han the pressure below, the macroadenoma then delivers itself into the sphenoid sinus. Intra-operative MRI was performed in an experimental setting to determine whether the neurosurgeon had successfully removed all of the tumor. Because using this surgical approach means a limited field-of-view, it
34、is important to know beforehand what it is you are operating on. As we will see there are lesions you do not want to operate using this approach!Another common pathway of extension is laterally into the cavernous sinus. It is not always possible to tell if there is cavernous sinus invasion, but ther
35、e are three signs to look out for: -Is there more than 50% encirclement of the carotid artery? Note: meningiomas tend to constrict the carotid artery, macroadenomas do not. -Is there lateral displacement of the lateral wall of the cavernous sinus compared to the opposite side? -Is there an increased
36、 amount of tissue interposed between the carotid artery and the lateral wall of the cavernous sinus? At medical school they teach you that a rare manifestation of a common lesion is more likely than a rare abnormality. Since pituitary adenomas are the most common lesions of the skull base, it is pru
37、dent to always include them in the differential diagnosis if you can not identify a normal pituitary gland when confronted with a mass in this region. This patient presented with nasal obstruction. She went to an ENT specialist who saw a large endonasal mass and she was referred to the neurosurgeon
38、for planned major skull base resection. The neurosurgeon had seen something similar before, and checked her prolactin-level. This was 4000 (25 or less is normal). Endonasal biopsy revealed prolactinoma. After treatment with bromocriptine the mass shrunk down and no surgery was necessary. Rathke Clef
39、t CystRathkes cleft cyst is the second of three pathologies derived from Rathkes cleft epithelium. The cyst is fluid-filled and has very thin walls with a thickness of only one or two cell layers.This is illustrated by the microscopic image. These walls can contain cells which secrete fluid, allowin
40、g the cyst to grow and compress adjacent structures.Rathkes cleft cysts can occur either in or above the sella turcica. On the images above there is a normal pituitary gland, a normal optic chiasm and a normal carotid artery on each side. The pituitary stalk is not identifiable, however, due to a ro
41、und mass in this area. The mass has a high signal intensity on the unenhanced T1-images. Now the only two things that are this bright on unenhanced T1-weighted images are either fluid (blood or proteinacious fluid) or fat. Solid masses are not this bright. Therefore it is most likely a cystic struct
42、ure originating from the pituitary stalk, probably a Rathkes cleft cyst. A cystic craniopharyngioma is also in the differential diagnosis. These images illustrate the importance of unenhanced T1 images.They allow you to appreciate that the abnormality is located in the pituitary stalk alone. If you
43、were only presented with images after the administration of intravenous contrast, you might think the pituitary gland was abnormal as well. These T1, T2 and T1-weighted images after gadolinium demonstrate another Rathkes cleft cyst located in the pituitary gland. Unlike the normal pituitary tissue a
44、nd pituitary stalk it does not enhance after the administration of intravenous contrast. The normal pituitary tissue is compressed and displaced far to the left. It is important to recognize this as it could be mistaken for an enhancing component of the cystic mass. In general, all extra-axial masse
45、s , i.e. masses outside of the brain like the pituitary gland and stalk, will enhance because they do not have a blood-brain barrier. If you have a non-enhancing extra-axial mass, there are three possibilities: 1. Rapid arterial flow (eg. large blood vessel). 2. No cellular tissue (eg. cyst). 3. No
46、blood supply (eg. infarcted mass). CraniopharyngiomaCraniopharyngioma is the third of the three pathologies derived from Rathkes cleft epithelium. Technically these are benign tumors, but unlike Rathkes cleft cysts, they have thick walls and are locally invasive. Macroscopically, it is a complex mas
47、s with multiple nodules at the base of the brain, sinuating along the fissures. Often, it can not be completely resected. The picture on the right shows a thick-walled cyst as part of the craniopharyngioma. In over 50% of cases craniopharyngiomas have a pathognomonic appearance. On these unenhanced
48、and enhanced T1-weighted sagittal images, a compressed pituitary gland can be identified. There is a large intrasellar and suprasellar mass with cystic and enhancing components as well as calcifications. These findings in a child are virtually pathognomonic for craniopharyngioma (perhaps with only a
49、 dermoid in the differential diagnosis). Coronal images of the same mass. And axial images. Unenhanced CT shows the calcifications more clearly. After intravenous contrast the total extent of the lesion and its cystic components are much less evident. MeningiomaThe most common intracranial tumor in adults is the meningioma with 20% of occurring at the skull base. This is an autopsy specimen with the brain removed, showing a meningioma sitting on the diaphragma sellae. Meningiomas are almost always solid lesions, sometimes with a cyst on the edge. They
