Download Imaging of the Pituitary Gland

Imaging of the Pituitary Gland
Kirsten Forbes, MD
John Karis, MD
William L. White, MD†
This article reviews the magnetic resonance imaging techniques that can be
used to assess the pituitary gland and describes the imaging characteristics of
normal sellar anatomy and common sellar and suprasellar pathologies.
Key Words: macroadenomas, magnetic resonance imaging, microadenomas, pituitary
Divisions of Neuroradiology and †Neurosurgery, Barrow Neurological Institute, St. Joseph’s Hospital
and Medical Center, Phoenix, Arizona
ndoubtedly, magnetic resonance
(MR) imaging is the optimal imaging technique for evaluating the
pituitary gland. Adequate assessment
requires dedicated high-resolution imaging through the sellar region. The
coronal plane offers the best single view
for assessing the sella and allows the pituitary gland to be distinguished from
the surrounding structures. Sagittal
views are particularly helpful for evaluating midline structures. Because the
pituitary gland is small,high spatial resolution images are required. Slice thicknesses must be 3 mm or less, and the
field of view must cover only the sellar
and immediate parasellar regions. T1weighted sequences, with and without
gadolinium, are optimal for evaluating
both normal anatomy and underlying
pathology. The amount of gadolinium
used is field-strength dependent with a
one-half dose typically being used at 1.5
Tesla. Fat-saturation techniques are
useful for postoperative evaluations.14
U
Normal Anatomy
The anterior and posterior lobes of
the pituitary can often be differentiated
on MR imaging. In adults the anterior
lobe is isointense to the remainder of
the brain, and the posterior lobe is hyperintense on T1-weighted sequences
(Fig. 1).11 This finding is thought to
reflect the high concentration of neurosecretory granules in the neurohypophysis, but the exact substrate is still debated. In neonates and during pregnancy,
distinguishing the anterior from the
posterior pituitary may be challenging
because the anterior lobe also appears
hyperintense on T1-weighted images.
Absence of the normal posterior pi-
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Forbes et al: Imaging of the Pituitary Gland
A
B
C
D
Figure 1. (A) Sagittal precontrast T1-weighted image reveals a normal-appearing pituitary gland. The adenohypophysis is isointense
and the neurohypophysis is hyperintense. (B) Sagittal postcontrast T1-weighted image shows normal diffuse enhancement of the
gland. (C) Coronal precontrast T1-weighted image facilitates identification of the infundibulum, optic chiasm, and cavernous sinuses.
(D) Fat-saturated coronal postcontrast T1-weighted image is useful for assessing the gland for residual tumor or a recurrence after surgery.
tuitary bright spot should prompt a
search for an ectopic posterior pituitary
that has failed to migrate inferiorly
from the hypothalamus (Fig. 2). This
finding can also be associated with
transection of the pituitary stalk. However, absence of the pituitary bright
spot can be a normal finding or may
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BARROW QUARTERLY • Vol. 18, No. 3 • 2002
reflect technical factors. It should not
be interpreted as an absolute indication
of pathology.
The size of the pituitary gland varies
with physiological status. In the normal state, the gland is less than 8-mm
high. During puberty or pregnancy, it
becomes larger and more upwardly
convex (Fig.3). During puberty it may
reach 10-12 mm in females and exhibits even more marked changes during pregnancy.9 Chanson et al. report
that the pituitary height exceeds 9.0
mm in less than 0.5% of healthy
women age 18-35.3 They report one
healthy 24-year-old female with a nor-
Forbes et al: Imaging of the Pituitary Gland
A
B
Figure 2. (A) Sagittal and (B) coronal precontrast T1-weighted images show a hyperintense region just below the hypothalamus. The
normal pituitary bright spot is absent in the sella turcica, consistent with an ectopic posterior pituitary gland.
A
B
Figure 3. During puberty and pregnancy the pituitary gland undergoes physiological hypertrophy and shows a convex upper margin,
as seen on (A) sagittal T1-weighted and (B) coronal T2-weighted images.
mal pituitary gland height of 12 mm
and width of 12 mm. Another female
patient with a normal pituitary gland
measured 16 mm in width. They emphasized that physiological pituitary
hypertrophy seems to be a frequent
cause of incidentaloma and that careful
examination of the MRI may help distinguish this entity from pituitary tu-
mors and infiltrating lesions.Physiological pituitary hypertrophy is confirmed
by normal baseline pituitary function
and extensive hormonal tests. Identification of these patients is important to
avoid unnecessary pituitary surgery.3 It
is normal for the pituitary gland to be
markedly flattened against the floor of
the sella, a configuration known as an
empty sella turcica (Fig. 4). The sella
largely becomes filled with cerebrospinal fluid (CSF) because of the enlarged
diaphragmatic sella hiatus, and it may
appear to expand with CSF pulsations.
Pituitary Microadenomas
The findings associated with a pituitary microadenoma on MR imaging
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Forbes et al: Imaging of the Pituitary Gland
Figure 4. The empty sella turcica, shown in this sagittal T1weighted image, is a normal anatomic variant. An incidental
basilar artery aneurysm is present.
A
B
Figure 5. (A) Coronal T1-weighted image shows an upward convexity of the left pituitary gland. Within the gland, a focal area of hypointensity is seen. (B) After intravenous contrast is administered, the microadenoma remains hypointense while the remainder of the
gland enhances.
are often subtle, necessitating a highquality imaging study (Fig. 5). With optimal MR technique,about 90% of these
small tumors (10 mm or less in diameter)
can be identified.14 False-negative studies are most often associated with Cushing’s disease because many tumors that
secrete adrenocorticotropic-hormone
(ACTH) are small. A microadenoma
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BARROW QUARTERLY • Vol. 18, No. 3 • 2002
can alter the contour of the pituitary
gland, creating an outward convexity of
its superior or inferior aspects. Classically,tumors secreting ACTH,thyroid stimulating hormone, luteinizing hormone,
and follicle stimulating hormone are
found centrally within the pituitary
gland while prolactin and growth hormone adenomas occur at the periphery.
Laterally placed microadenomas may
cause the infundibulum to deviate from
the tumor. However, a tilted infundibulum can also be a normal finding observed in about 50% of normal subjects.1
Pituitary microadenomas are easier
to identify on T1-weighted sequences
than on T2-weighted sequences because
they are often isointense to normal pitu-
Forbes et al: Imaging of the Pituitary Gland
A
B
Figure 6. (A) Sagittal T1-weighted noncontrast images show diffuse signal hyperintensity throughout the pituitary gland consistent
with subacute hemorrhage. (B) Coronal T1-weighted sequences confirmed the findings.
itary tissue on the latter. On T1-weighted sequences, microadenomas tend to
appear as focal hypointense lesions. Occasionally, they are isointense or even
hyperintense to the surrounding pituitary. Susceptibility artifacts from the interface between the sphenoid sinus and
sella may project as low signal foci in the
pituitary gland and can mimic a microadenoma.10 Administration of intravenous gadolinium improves sensitivity,
particularly when lesions are isointense
on precontrast T1-weighted imaging.17
Compared to the normal pituitary
gland, microadenomas show delayed
gadolinium uptake. They are best detected by imaging immediately after
contrast administration when they appear as an area of relative nonenhancement. Some centers use dynamic MR imaging during contrast
administration, and this technique
may improve sensitivity slightly.4 The
time of maximal signal difference between microadenoma and normal
gland is variable although it occurs
within a few minutes of contrast administration.4 Imaging more than 30
minutes after intravenous contrast also
may help detect microadenomas,
which then appear as focal hyperin-
tense lesions relative to the surrounding gland.8 This technique, however, is
rarely used because delayed imaging is
impractical.
Pituitary Macroadenomas
Because macroadenomas are larger
than 10 mm in diameter, they are easier to detect radiologically than microadenomas. These benign tumors
often enlarge the sella turcica, a finding
that can be appreciated on plain radiographs and cross-sectional imaging.
On noncontrast T1-weighted imaging,
these intrinsic pituitary tumors are hypointense to the surrounding gland.
They exhibit heterogeneous enhancement after gadolinium administration.
On T2-weighted sequences, they are
more often hyperintense than microadenomas,particularly if they are soft or
necrotic.19 About 20 to 30% of adenomas show evidence of hemorrhage.23
Subacute hemorrhage is best appreciated on T1-weighted sequences where it
appears as hyperintense methemoglobin (Fig. 6). Signal intensity on T2weighted imaging is variable. Typically,
hemorrhage is asymptomatic although
it may cause clinical symptoms of pituitary apoplexy.18,21
As the pituitary macroadenoma enlarges, it has a tendency to invade surrounding structures. Superior extension into the suprasellar cistern is well
demonstrated on MR imaging, which
allows compression of the optic chiasm to be assessed (Fig. 7). Tumor invasion of the cavernous sinus is more
difficult to determine; traditionally, the
presence of tumor lateral to the internal carotid artery is a reliable sign
(Fig. 8).6 Encasement of the intercavernous internal carotid artery by adenoma greater than or equal to 67%
was concluded to be a specific sign of a
cavernous sinus invasion in one study. 6
Extrinsic narrowing of the carotid artery is rarely associated with pituitary
adenomas and is more suggestive of
meningiomas. Tumor also may extend
inferiorly into the sphenoid sinus or
clivus with a predisposition to erode
bone. As a result, the hyperintensity of
the clival bone marrow on T1-weighted images is lost.
MR imaging is a useful technique
for following macroadenomas. The
appearance after transsphenoidal surgery depends on the packing materials
used. Fat packed in the surgical defect
appears hyperintense on T1-weighted
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Forbes et al: Imaging of the Pituitary Gland
A
B
C
D
Figure 7. (A) Coronal T1-weighted precontrast image reveals a large intrinsic pituitary mass extending into the suprasellar cistern.
(B) After contrast administration, the mass shows strong heterogeneous enhancement. The optic chiasm is compressed. (C) Postcontrast sagittal image shows enlargement of the sella turcica. (D) Coronal T2-weighted image shows heterogeneous areas of signal
hyperintensity within the gland, indicating areas of cystic necrosis.
sequences and requires the use of fatsaturated sequences to distinguish contrast enhancement from packing material. The MR imaging signal from
Gelfoam is variable although it is often
isointense to the pituitary gland with a
hypointense center.7 Both types of
packing material show significant atrophy over time. Thus follow-up imaging is key for determining the presence
of residual tumor.
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Differential Diagnosis of
Pituitary Tumors
There is a wide differential diagnosis for mass lesions within the sellar
and suprasellar regions, including not
only tumors but also inflammatory
and vascular lesions.
Craniopharyngiomas and Rathke
cleft cysts share the same embryological
origin, the craniopharyngeal duct.
Most craniopharyngiomas are centered
on the suprasellar cistern. Occasionally,
they are located entirely within the
sella or third ventricle.16 The classic
form, the adamantinomatous craniopharyngioma, almost always contains
cystic components, which appear hyperintense on T1-weighted images because of their high cholesterol content
(Fig. 9). Adamantinomatous tumors
also usually contain solid enhancing
components as well as calcification,cre-
Forbes et al: Imaging of the Pituitary Gland
A
B
Figure 8. (A) Sagittal precontrast T1-weighted image shows that the normal hyperintense clivus has been invaded extensively and replaced with hypointense pituitary tumor. A small focus of hemorrhage is seen anteriorly. (B) Postcontrast axial image shows bilateral
invasion of the cavernous sinuses with tumor surrounding both internal carotid arteries.
A
B
Figure 9. (A) Sagittal T1-weighted precontrast image reveals a hyperintense suprasellar cystic lesion consistent with an adamantinomatous craniopharyngioma. (B) Coronal T2-weighted image shows evidence of optic chiasm compression.
ating a heterogenous appearance on
MR imaging. In contrast, papillary
craniopharyngiomas, which are most
often found in adults, are usually solid
enhancing lesions in the third ventricle.
Rathke cleft cysts are well-defined,
round lesions often found in the pars
intermedia of the pituitary gland. Their
appearance on MR imaging reflects
their composition. On T1-weighted
images, they are hyperintense if they
contain cholesterol-high mucoid material (Fig.10) and hypointense if they contain serous fluid.15 Calcification and en-
hancement are both extremely unusual.
About 10% of meningiomas occur
in the parasellar region, arising from
several locations including the tuberculum sellae, cavernous sinus, and
sphenoid wing.22 These tumors tend
to lie somewhat eccentric to the sella,
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Forbes et al: Imaging of the Pituitary Gland
A
B
Figure 10. (A) Sagittal and (B) coronal noncontrast T1-weighted images reveal an asymptomatic hyperintense focal lesion within the
pars intermedia consistent with a Rathke cleft cyst.
A
B
Figure 11. (A) Coronal postcontrast T1-weighted image reveals a homogeneously enhancing tumor within the left cavernous sinus,
extending into the sella turcica. (B) On the axial postcontrast image, an enhancing dural tail is visible consistent with a meningioma.
rather than arising from it. They are
often associated with a thick adjacent
dural tail. Although hyperintensity on
T1- and T2-weighted images can be
variable, meningiomas show strong
homogeneous enhancement after
contrast administration (Fig. 11). Associated hyperostosis and calcification
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can be detected by MR imaging but
are better assessed by computed tomography (CT).
Germinomas are also strongly enhancing homogeneous tumors found
in the suprasellar region (Fig. 12).13
They may occur primarily in the suprasellar region or as a metastatic de-
posit from a pineal region tumor.20
This midline germ-cell tumor can involve the infundibulum, hypothalamus, or anterior third ventricle and
often appears hyperdense on noncontrast CT.
Epidermoid and dermoid tumors
are benign tumors thought to arise
Forbes et al: Imaging of the Pituitary Gland
A
B
Figure 12. (A) Coronal and (B) sagittal postcontrast T1-weighted images reveal a somewhat ill-defined, homogeneously enhancing
tumor in the suprasellar region. Pathology confirmed a germinoma.
A
B
Figure 13. (A) Sagittal and (B) coronal postcontrast T1-weighted images show an ill-defined suprasellar mass with a thickened, enhancing infundibulum caused by metastatic lung carcinoma.
from inclusion of epithelium during
closure of the neural tube. Epidermoids
are often located lateral to the midline
and insinuate around adjacent structures. They are typically hyperintense to
CSF on proton-density and diffusionweighted imaging, which helps differentiate them from arachnoid cysts. Enhancement and calcification are both
rare. Dermoid tumors are most often
found in children and are located in the
midline. They appear heterogeneous
because of the presence of dermal appendages and squamous epithelium.
Metastatic disease can involve the
pituitary gland, particularly in patients
with advanced breast or bronchogenic
carcinoma (Fig. 13). These lesions can
occur in the sella or adjacent structures
and are commonly associated with
bone destruction.
Granular cell tumors are rare primary tumors located within the neurohypophysis. Although small nodules
of granular cell proliferation are common in this region at autopsy, symptomatic tumors are extremely unusual.
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Forbes et al: Imaging of the Pituitary Gland
B
A
Figure 14. (A) Pre- and (B) postcontrast T1-weighted images reveal an enhancing mass arising from the infundibulum. Pathology
confirmed a granular cell tumor.
A
B
Figure 15. (A) Coronal postcontrast T1-weighted image reveals an enhancing, thickened infundibulum. (B) Axial image also shows evidence of left frontal parenchymal enhancement as well as posterior dural enhancement, consistent with neurosarcoidosis.
This tumor shows contrast enhancement on T1-weighted imaging and
has a somewhat heterogeneous appearance on T2-weighted imaging
(Fig. 14).
Inflammatory lesions such as lymphocytic hypophysitis and sarcoidosis
cause thickening and enhancement of
the infundibulum. Lymphocytic hy-
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pophysitis likely results from an autoimmune process and almost exclusively occurs in peripartum women.
MR imaging shows diffuse enlargement of the anterior lobe of the pituitary gland associated with contrast
enhancement.12 On MR imaging, sarcoidosis tends to be associated with
other intracranial findings, including
multiple intraparenchymal or duralbased enhancing lesions and meningeal
enhancement (Fig. 15).5
Aneurysms arising from the cavernous or supraclinoid segments of the carotid artery are extremely important
lesions to distinguish from pituitary
adenomas before surgery. On routine
T1-weighted spin-echo sequences,aneurysms are hypointense due to the
signal void produced by flowing
blood.2 When thrombosed, an aneurysm is hyperintense on T1-weighted
images. T2-weighted images can help
detect a laminated appearance, a useful
diagnostic feature of aneurysms. If
needed, MR angiography can be used
to confirm the diagnosis.
Conclusion
MR imaging is the optimal imaging
technique for assessing the sellar or suprasellar region. High-resolution imaging is required to evaluate the normal
anatomy and to detect subtle tumors
such as microadenomas. The differential diagnosis of pituitary adenomas is
wide and includes not only other primary and secondary tumors but also inflammatory and vascular lesions.
Forbes et al: Imaging of the Pituitary Gland
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