MRI of the Orbit and Sella Turcica

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Questions and Answers

Which of the following bones does not form the floor of the orbit?

Sphenoid

Zygomatic (correct)

Palatine

Maxilla

What structure separates the orbit from the underlying maxillary sinus?

Frontal bone

Ethmoid bone

Lacrimal bone

Maxilla (correct)

What is the name of the infection of fat and muscles around the eye?

Orbital cellulitis (correct)

Retro-orbital lesions

Retinoblastoma

Optic disc distortion

Which of the following is not a reason for performing an MRI of the orbits?

To diagnose a fracture of the zygomatic bone (A) Signup and view all the answers

Which of the following best describes the shape of the orbit?

Pyramidal (B) Signup and view all the answers

Which bone separates the orbit from the anterior cranial fossa?

Frontal bone (A) Signup and view all the answers

Which structure within the orbit contains the optic nerve?

Optic canal (B) Signup and view all the answers

What is the recommended patient position for an MRI of the orbits?

Supine (D) Signup and view all the answers

Which of the following indications for a pituitary region assessment might require a MRI procedure?

All of the above (D) Signup and view all the answers

What is the correct patient position for a pituitary region MRI?

Supine, with the head first in the coil (C) Signup and view all the answers

Which of the following is the correct coverage area for a coronal localizer during a pituitary region MRI?

All of the Above (D) Signup and view all the answers

Which of the following is NOT a critical alignment requirement for a sagittal localizer during a pituitary region MRI?

Parallel to the sphenoid sinus (C) Signup and view all the answers

Why is it important to immobilize the patient with sponges and straps during a pituitary region MRI?

To prevent motion artifacts during image acquisition (A) Signup and view all the answers

What is the recommended position for the patient during an MRI of the orbits?

Supine with the head tilted forward (D) Signup and view all the answers

What is the purpose of the axial localizer in an MRI of the orbits?

To obtain coronal slices (C) Signup and view all the answers

What is the recommended alignment for coronal slices in an MRI of the orbits?

All of the above (D) Signup and view all the answers

What is the purpose of the diaphragm sellae?

To protect the pituitary gland (D) Signup and view all the answers

What is the most important reason for using an eye mask during an MRI of the orbits?

To minimize ocular movement that can degrade image quality (D) Signup and view all the answers

What is the name given to the raised anterior border of the sella turcica?

Tuberculum sellae (A) Signup and view all the answers

What is the significance of the pituitary gland in the body?

It produces hormones that regulate growth and development. (A) Signup and view all the answers

Why is a systematic approach to the pituitary region crucial?

To detect small lesions that can have a significant impact on the patient (C) Signup and view all the answers

Study Notes

MRI of the Orbit and Sella Turcica

Anatomical Overview: The orbits are bilateral, symmetrical bony cavities in the head, enclosing the eyeball and associated structures. They are pyramidal, with the apex pointing posteriorly and the base situated anteriorly. The orbit's boundaries are formed by seven bones.
Bony Orbit Structures: The bones comprising the bony orbit include the frontal, sphenoid, lacrimal, ethmoid, maxilla, and zygomatic bones. These are illustrated in Figures 1, 4, 5.
Sella Turcica (Pituitary Region): The Sella Turcica, a saddle-shaped depression in the sphenoid bone, houses the pituitary gland, a vital part of the endocrine system. It's bounded by the tuberculum sellae (anterior portion), dorsum sellae (posterior portion), and the hypophyseal fossa. A protective layer, the diaphragm sellae, covers the pituitary gland. Figure 3 and 17 illustrate the structure.

Indications (MRI of Orbit and Sella Turcica)

Retro-orbital Lesions: Lesions behind the eye.
Optic Disc Distortion or Pallor: Damage to optic nerve axons, occurring in various disorders.
Orbital Cellulitis: Infection of orbital fat and muscles.
Intra-ocular Lesions: Lesions within the eye.
Retinoblastoma: A type of eye cancer.

MRI Procedure (Orbit)

Patient Position: The patient is positioned supine (head first). Remove all eye makeup. Align the chin using the Orbital-meatal line (+15 to table top), ensuring the optic nerve is perpendicular to the table. Turn on alignment lights. Place the sagittal light on the mid-sagittal line of the patient's head and the axial line to pass through.
Coils and Immobilization: Position coils near the eye without touching the patient. Immobilize using sponges and straps. Ask patients to close their eyes during acquisition to limit motion artifacts.
Scout Slice Placement: Obtain axial slices using a coronal localizer. Align the slices parallel to a line drawn through the inferior orbital margins.. Obtain coverage from superior to inferior (inferior orbital margin to superior), lateral to medial (zygoma to zygoma) and posterior to anterior (pons to anterior globes).
Axial Localizer for Coronal Slices: Use an axial localizer for coronal slices. Align the scan parallel to a line connecting posterior orbital margins and perpendicular to the cribriform plate. Obtain coverage as per axial scans.

MRI Procedure (Sella Turcica/Pituitary)

Patient Position: Similar to orbits protocol, ensure the patient is supine (head first).
Scout slice placement: Use a coronal localizer to obtain sagittal slices; position parallel to falx cerebri.
Coverage: Obtain coverage from floor of sphenoid sinus to genu of corpus callosum; laterally, from cavernous sinus to cavernous sinus; posteriorly, from ventral aspect of pons to anterior clinoid.
Sagittal Localizer for Coronal Slices: Use a sagittal localizer to get a coronal slice with alignment directly perpendicular to the floor of the sella on sagittal images. Obtain coverage as per sagittal plane.

MRI Sequences

Orbit: Included sequences include axial (T2 Flair), axial (T1 Flair) (FS), axial (T1) (Flair) (FS) (post GAD), and coronal (T1) (Flair) (FS) (post GAD). Specific parameters like TR, TE, FA, ETL, and slice thickness are detailed in the provided table.
Pituitary: Included sequences include sagittal (T1WI) SE, coronal (T2WI) FSE, coronal (T1WI) SE, coronal (T1WI) SE (post GAD), sagittal (T1WI) SE (post GAD), and coronal [(T1WI)-Dyn study (post GAD)]. Table with specific parameters is provided..

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Description

This quiz covers the anatomical overview of the orbits and sella turcica, emphasizing the structures and bones that form these regions. It also addresses the significance of the pituitary gland housed within the sella turcica. Prepare to test your knowledge on the MRI indications and structures involved.