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1、.The Radiology AssistantHomeAbdomenBreastCardiovascularChestHead NeckMusculoskeletalPediatricsNeuroradiologyMiscellaneousCasesTop SitesNewsletter Sella Turcica and Parasellar Regionby Walter Kucharczyk and Marieke HazewinkelRadiology department of the University of Toronto, Canada and the Radiology
2、department the 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
3、to overview 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 cli
4、cking on one 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 Approa
5、ch to Differential 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.
6、 If it is in 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 Differe
7、ntial Diagnosis. 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
8、common abnormalities that arise in the pituitary gland are pituitary adenoma, Rathkes cleft cyst and craniopharyngioma. 精品.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
9、the bottom and thicker 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 gra
10、nulomas. In adults 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
11、 tumors to originate 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 thi
12、s location is the 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
13、internal carotid 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
14、cranially to the 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
15、midline. 精品.Cavernous 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
16、 common pathologies 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
17、of the cavernous sinus.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 inflammato
18、ry pathologies occur 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
19、and bone.Posterior 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 a
20、rise in the clivus 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 mic
21、roadenomas are less 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 diffe
22、rential diagnosis: 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 w
23、ith a negative scan 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 med
24、ical therapy or pituitary disease not amenable to medical therapy such as Cushings disease) it is necessary to give contrast to localize the lesion as accurately as possible.精品.On an unenhanced scan, approximately 70% of all pituitary microadenomas can be detected. If you give gadolinium, you can re
25、duce the false-negative 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
26、intravenous contrast. 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 gro
27、w, they first expand the 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
28、. This is one feature 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
29、of a pituitary macroadenoma. 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. 精品.The usefulness of observing the in
30、clination of the diaphragmatic 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 th
31、e leaflets in the other direction (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
32、enhancement after the administration 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 a
33、bove the dura is larger than 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 l
34、imited field-of-view, it 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!精品.Another common pathway of extension is laterally into the cavernous sinus. It is not always possible to tell if there is cavern
35、ous sinus invasion, but there 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
36、side? -Is there an increased 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
37、of the skull base, it is prudent 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 r
38、eferred to the neurosurgeon 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 surger
39、y was necessary. Rathke Cleft 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
40、which secrete fluid, allowing 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 identi
41、fiable, however, due to a round 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
42、 most likely a cystic structure 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 pi
43、tuitary stalk alone. If you were only presented with images after the administration of intravenous contrast, you might think the pituitary gland was abnormal as well. 精品.These T1, T2 and T1-weighted images after gadolinium demonstrate another Rathkes cleft cyst located in the pituitary gland. Unlik
44、e the normal pituitary tissue and 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
45、 general, all extra-axial masses , 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 cel
46、lular tissue (eg. cyst). 3. No 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. Macro
47、scopically, it is a complex mass 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 a
48、ppearance. On these unenhanced 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 dermoid in the differential diagnosis). 精品.Coronal images of th