- male: 8 mm
- female: 9 mm
- pregnancy: 12 mm
Systematic approach to interpretation
As with all studies, having a systematic approach to the pituitary region is essential if subtle lesions are to be detected. There is no single correct way to do this, and what is presented is merely a personal approach.
Key structures to identify and assess in every study include:
- pituitary gland including posterior pituitary bright spot and infundibulum
- optic nerves, chiasm, and tracts
- diaphragma sellae and boundaries of the pituitary fossa
- boundaries of the cavernous sinus and Meckel's cave
- internal carotid arteries and branches
- dynamic enhancement of the pituitary
The pituitary gland itself should be examined to ensure that it is age-appropriate in size and normal in signal (see above). The infundibulum should be midline and the posterior pituitary bright spot should be sought, although it is not always visible (ectopic posterior pituitary should be carefully sought in those patients where a normal posterior pituitary bright spot is not evident).
The dynamic enhanced coronal images should be viewed in such a way as to view the wash in of contrast at each location. Depending on the PACS system used and the scanning protocol this can be tricky.
The optic nerves, optic chiasm, and optic tracts should be carefully assessed as even small lesions can lead to visual symptoms, which are a common indication for imaging of this area. The relationship of the chiasm to the pituitary is important and a prefixed (located above the tuberculum sellae) or postfixed (located above the dorsum sellae) chiasm should be identified 2 .
Extreme care should be taken in ensuring that there are no compressive lesions such as a 2-3 mm meningioma. The optic nerves should be followed as far anteriorly as possible on coronal T2 images (if obtained) to assess for the presence of increased signal within the nerve.
Following this, the boundaries of fossa should be examined to ensure that the fossa is not enlarged or eroded (previous mass, hydrocephalus, intracranial hypertension). At this time, the bone marrow signal in the clivus should be assessed (see: normal bone marrow signal of the clivus).
The cavernous sinuses and Meckel's caves should be examined for symmetry and normal anatomy. The visible arteries should all be inspected for obvious aneurysms or malformations; this is best done on T2 weighted imaging if provided. Although no dedicated arterial imaging is present, finding an asymptomatic aneurysm can be a life-saving event. In contrast, missing an obvious aneurysm which later ruptures is a tragedy. Particularly relevant regional aneurysms include anterior communicating artery aneurysms, medially projecting "carotid cave" aneurysm, superiorly projecting ophthalmic artery aneurysms, terminal internal carotid artery aneurysms, posterior communicating artery aneurysms and basilar tip aneurysms.
It is also crucial to identify an aberrant course of the carotid or other aberrant vessels, especially if surgery is likely.
Finally, the rest of the imaged brain should be reviewed for unexpected findings.
Pituitary masses
Assessment of pituitary masses is simplified by taking into consideration the overall pattern (both location, morphology and signal) as well as looking for specific signs.
Patterns
Masses of the pituitary and immediate surrounds present in only a limited number of patterns, which are helpful in narrowing the differential. The two main groups to think of are patterns of morphology and patterns of location.
- solid and enhancing pituitary region mass
- mixed cystic and solid pituitary region mass
- cystic pituitary region mass
Pattern of location:
- purely intrasellar pituitary mass
- purely suprasellar
- both supra and intrasellar
A couple of additional coexisting patterns which are worth considering are:
- pituitary region mass with intrinsic high T1 signal
- abnormal enhancement/bulkiness of the pituitary infundibulum
Helpful signs
In addition to identifying the dominant imaging pattern, close attention to a number of signs can dramatically aid you in narrowing the differential:
- dural tail: meningioma, hypophysitis, and metastases
- diaphragma sella displacement: up vs. down
- carotid narrowing: meningioma
- erosion of sella (rather than remodeling): metastasis
- identify pituitary as separate usually implies non-adenoma
What clinicians want to know
In addition to a general description of any identified mass and the likely diagnosis, there are a number of features which should be specifically commented upon, especially if you believe surgery is likely to be indicated. These include:
- mass
- size in three dimensions
- presence of necrotic/cystic areas
- size of diaphragmatic opening and size of the suprasellar component:
- a narrow waist of the tumor where it passes through the diaphragm may limit the amount of tumor which can be removed via a transsphenoidal approach and whether the tumor will come down at surgery with Valsalva or air into a lumbar drain
- this occurs in front of the tumor (visible as a little cleft of CSF in front of the mass)
- presence of this space increases the likelihood of an intraoperative CSF leak
- medially located or aberrant carotid arteries
- aneurysms or other visible vascular anomalies especially in the cavernous sinuses
- entering an artery transsphenoidally will not bode well for the patient, the surgeon or the radiologist
- size of the bony sella, expanded or not, is useful, gives you an idea of the size of the surgical corridor
- degree of pneumatization of the sphenoid, location of the sphenoid septum and any anomalous sinus anatomy
- this is best assessed by CT but is visible also on post-contrast coronal T1 images
- the location of sphenoid septum helps guide the transsphenoidal approach and ensures that the pituitary fossa is entered rather than adjacent cavernous sinus or orbit
