Download Part I - Revising the sellar and parasellar region: normal anatomy

Part I - Revising the sellar and parasellar region: normal
anatomy
Poster No.:
C-0182
Congress:
ECR 2015
Type:
Educational Exhibit
Authors:
I. Candelaria, C. Figueira, C. M. Oliveira, S. P. F. P. Basso, F.
Caseiro Alves; Coimbra/PT
Keywords:
Neuroradiology brain, Anatomy, CT, MR, Diagnostic procedure,
Normal variants, Congenital, Pathology
DOI:
10.1594/ecr2015/C-0182
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Learning objectives
Our objective is to provide an insight of the sellar and parasellar regions normal anatomy,
on both CT and MRI.
Background
The sellar and parasellar regions are anatomically and pathologically complex areas.
Expert knowledge of its normal anatomy and spectrum of disease is important to provide
focused differentials and guide patient management.
THE SELLAR REGION
The sella turcica is a concave depression in the sphenoid bone. Its ventral borders are the
tuberculum sellae and anterior clinoid processes, and its dorsal borders are the dorsum
sellae and the posterior clinoid processes.
The roof of the sella consists of a thin dural covering - the diaphragma sellae.
Within the sella turcica lies the pituitary gland which consists of the ventral
adenohypophysis and the dorsal neurohypophysis.
The adenohypophysis: formed by ascending cells of the Rathke pouch, it comprises
three parts - pars distalis, pars intermedia and pars tuberalis. The adenohypophysis is
responsible for secretion of regulatory hormones (prolactin, growth, adrenocorticotropic,
follicle stimulating, luteinizing and thyroid stimulating hormones).
The neurohypophysis: results of an evagination or extension of the floor of the third
ventricle. It is composed of two parts - the pars nervosa and the infundibulum (which
inserts into the median eminence of the hypothalamus). This part of the pituitary gland
primarily consists of axon terminals that secret hormones formed in the hypothalamus
(anti-diuretic hormone and oxytocin).
THE PARASELLAR REGION
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It generally encompasses the cavernous sinuses and the suprasellar cistern structures.
The basisphenoid and sphenoid sinuses are also included.
The cavernous sinuses: consists of trabeculated, multilobulated venous channels which
lie lateral to the sella turcica and sphenoid sinus. Cranial nerves III, IV, V1 and V2 lie
within the lateral dural wall, whereas the VI cranial nerve lies within the cavernous sinus.
It also contains the cavernous segment of the internal carotid artery.
The suprasellar cistern: contains the optic chiasm (nerves), the anterior third ventricle,
the hypothalamus and tuber cinereum. The anterior margin of the hypothalamus consists
of the lamina terminalis and it's posterior margin is imprecise, demarcated as a vertical
plane extending from the mamillary bodies to the posterior comissure.
The tuber cinereum is a lamina of grey matter, located ventrally to the mamillary bodies.
These structures are part of the limbic system and are paired together, forming a lining
in the floor of the hypothalamus, which connects to the hippocampi via the fornices.
There are also two cerebrospinal fluid containing structures: the optic nerve recess
(ventral to the optic chiasm) and the more dorsal infundibular recess.
Images for this section:
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Fig. 1: Schematic representation of the sellar region. The pituitary gland lies within the
bony sellar.
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Fig. 2: Schematic representation of the sellar region, lateral view.
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Findings and procedure details
Computed tomography (CT) and magnetic resonance imaging (MRI) are complementary
modalities for evaluating the sellar and parasellar regions.
COMPUTED TOMOGRAPHY
CT represents the mainstay in the evaluation of the bony sella, allowing for a precise
delineation of its structure, determining if a process is primarily osseous in origin or results
of secondary involvement of the skull base (Figs. 3 and 4).
In addition, CT can also identify calcifications, which can be either vascular, dystrophic
or tumoral in origin.
MAGNETIC RESONANCE IMAGING
MRI, due to its high contrast, allows for better depiction of the soft tissue structures which
are in direct contact with the bony sella. It is also important to recognize normal MR
imaging characteristics of the sellar and parasellar regions.
The various sequences in current MRI protocols can help determine wether a lesion solid,
cystic, hemorrhagic or fatty in origin, which further helps in narrowing of the differential
diagnosis.
The imaging protocol should also be tailored to the region of interest, which means
appropriate field of view and slice thickness. The use of gadolineum is determined on
clinical indication, such as tumoral characterization.
NORMAL FINDINGS
The adenohypophysis is isointense to the pons on sagittal imaging.
The neurohypophysis is usually hyperintense on T1, due to the presence of vasopressin
granules. However, if there is doubt regarding growth or endocrine abnormalities, follow
up MR should be done to exclude infiltrative or tumoral processes.
On dynamic imaging, due to the absence of a blood-brain barrier, the pituitary gland
and infundibulum usually enhance homogeneously and rapidly, only slightly hypointense
to the adjacent cavernous sinus. Normally, there is accumulation of contrast first in
the cavernous sinus, followed by the infundibulum and superior medial aspect of the
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hypophysis. As for the remaining adenohypophysis, it usually enhances in a centrifugal
fashion
Images for this section:
Fig. 3: CT image, sagittal view: Bone and soft tissue window representing fundamental
anatomic landmarks of the sellar region.
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Fig. 4: CT, Coronal plane, Pre and post contrast soft tissue window representing the
sellar and parasellar region.
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Fig. 5: Sagittal view. Pre and postcontrast fat saturated T1 weighted image depicting
normal MRI anatomy of the sellar and parasellar region.
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Fig. 6: Coronal view. Pre and post contrast fat saturated T1WI which also depicts normal
MRI anatomy of the sella turcica and surrounding structures. Although not shown, the
normal protocol usually includes a coronal view T2WI.
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Conclusion
Understanding the normal anatomy of the sellar and parasellar regions, although difficult,
allows for precise characterization of pathology which arises either from the bony or soft
tissue components of this structure.
Dedicated MRI protocols are important for complete characterization of the sellar
and parasellar regions, with CT considered as a complementary modality to evaluate
anatomic variants, calcification, or osseous extension.
Personal information
References
Chin, B., Orlandi, R., Wiggins, R., Evaluation of the sellar and parasellar regions,
Magnetic Resonance Imaging Clinics of North America, 2012, 20: 515-543
Fitzpatrick, M., Tartaglino, M., Hollander, M.D., Zimmerman, R.A., Imaging of sellar and
parasellar pathology, Radiology Clinics of North America, 1999, 37(1): 101-121.
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