Anatomy

• How many major sinus groups are there, and what bones contain them?
  There are four major groups: frontal (frontal bone), maxillary (maxillae), ethmoid (ethmoid bone), and sphenoid (sphenoid bone).
• How are the sinuses arranged relative to one another?
  Frontal sinuses lie superior to the orbits, maxillary sinuses lie inferior to the orbits, ethmoid air cells lie between the orbits, and the sphenoid sinuses lie posterior to the ethmoids beneath the sella turcica.
• How do the sinuses communicate with the nasal cavity?
  Each drains through small ostia into the nasal meatuses — the frontal and maxillary sinuses drain into the middle meatus, and the sphenoid drains into the sphenoethmoidal recess.
• Why must the sinuses be developed and aerated before they are visible radiographically?
  They begin forming at birth but are not fully pneumatized until adolescence; fluid-filled or undeveloped cavities appear opaque.
• How can sinus anatomy help locate fractures or infection?
  Opacification, mucosal thickening, or air-fluid levels indicate inflammation or trauma-related hemorrhage within a specific sinus cavity.

Positioning

• Why are sinus projections performed upright whenever possible?
  To demonstrate air-fluid levels and differentiate fluid from other pathology.
• Why must the central ray always be horizontal in sinus imaging?
  A horizontal beam ensures air-fluid levels can be detected.
• Why are both lateral sides of the sinuses not required, unlike nasal bones?
  All four sinus groups can be demonstrated on a single lateral image.
• Why is the Waters projection considered the “gold standard” for maxillary sinuses?
  It projects the petrous ridges just below the maxillary floors, giving an unobstructed view.
• Why is the open-mouth Waters projection performed?
  It shows the sphenoid sinuses projected through the open mouth, an alternative to SMV when hyperextension is not possible.
• Why is the SMV projection difficult for some patients?
  It requires extreme neck extension to bring the IOML parallel to the IR.
• Why must the MSP be perpendicular in sinus imaging (Caldwell, Waters, SMV)?
  To prevent rotation, which distorts symmetry of orbits, nasal septum, or sinuses.
• Why is the angled-grid Caldwell preferred over the vertical-grid version?
  It brings the IR closer to the patient, reducing OID and improving resolution.

Technique & Image Evaluation

• How do you know the IPL was perpendicular in the lateral sinus projection?
  The orbital roofs and mandibular rami are superimposed.
• How do you confirm the IOML was positioned correctly on the lateral?
  The sella turcica is in profile, and no tilt is present.
• How do you know the MSP was perpendicular on the Caldwell?
  The orbits and frontal sinuses appear symmetric side to side.
• What indicates the correct CR angle and positioning on the Caldwell?
  Petrous ridges are projected in the lower third of the orbits, and frontal sinuses are above the frontonasal suture.
• How do you know the chin was extended enough on a Waters projection?
  The petrous ridges are projected just below the maxillary sinuses.
• What error is indicated if the petrous ridges appear too high in a Waters?
  The chin was not extended enough.
• How do you check for rotation on a Waters projection?
  The orbits and maxillary sinuses should appear symmetric, with nasal septum aligned at midline.
• How do you know the patient was positioned correctly for the open-mouth Waters?
  Sphenoid sinuses are clearly projected through the open mouth, and petrous ridges lie immediately below the maxillary sinuses.
• What error is indicated if the mandible obscures the ethmoid sinuses on an SMV?
  The neck was not extended enough to make the IOML parallel with the IR.
• How do you confirm correct extension on the SMV?
  The mandibular condyles project anterior to the petrous ridges, and the mentum projects anterior to the ethmoid sinuses.

Clinical Applications

• Why are sinus series important in evaluating infection or trauma?
  They reveal mucosal thickening, fluid levels, or hemorrhage that suggest sinusitis or fracture communication with a sinus cavity.
• Why are sinus images sometimes used in pre-operative planning?
  They delineate the anatomy of the osteomeatal complex and aid ENT surgeons in image-guided procedures.
• Why is differentiation between sinusitis and neoplasm critical?
  Both can cause opacification, but neoplasms alter bone margins or cause expansion, requiring further imaging such as CT.
• How do upright sinus radiographs complement CT scans in modern practice?
  They provide functional information about air-fluid levels at a lower dose and can be obtained rapidly for follow-up or screening.
• Why must radiation protection and collimation be emphasized in sinus studies?
  The lenses of the eyes are radiosensitive; tight collimation and proper technique minimize unnecessary exposure.