The Posteroanterior (PA) View of the Skull (0° Central Ray) is the fundamental baseline projection for cranial radiography. Unlike the modified Caldwell projection (which uses a 15⁰ caudal tilt), the 0° PA baseline directs the X-ray beam perpendicular to the image receptor, providing an un-distorted view of the frontal bone, internal auditory canals, and symmetrical calvarial structures while minimizing radiation exposure to the eyes.

1. Clinical Indications & Contraindications

Detailed Indications:

• Frontal Bone Pathologies & Trauma: Detection of linear, depressed, or stellate fractures of the frontal bone, supraorbital margins, and frontal air sinuses.
• Calvarial Symmetry & Suture Analysis: Evaluation of the sagittal suture, coronal sutures, and craniosynostosis (premature suture fusion) in pediatric/adolescent cases.
• Neoplastic & Destructive Bone Lesions: Assessment of osteolytic or osteoblastic lesions, Multiple Myeloma (“punched-out” lytic lesions), and metastases in the cranial vault.
• Metabolic & Chronic Bone Diseases: Radiographic diagnosis of Paget’s disease (osteitis deformans), fibrous dysplasia, hyperparathyroidism (“salt-and-pepper” appearance), and hyperostosis frontalis interna.
• Intracranial Calcifications & Foreign Bodies: Identification and localization of radiopaque foreign materials, pineal gland calcifications, choroid plexus calcifications, and falx cerebri calcification.
• Evaluation of Crista Galli & Ethmoid Sinuses: Clear visualization of the perpendicular plate of the ethmoid, crista galli, and superior nasal septum.

Contraindications & Limitations:

• Unstable Cervical Spine Trauma: Absolute contraindication for prone or erect positioning. If a C-spine injury is suspected, never turn the patient face down or manipulate the neck; perform an AP 0° Supine / Trauma AP instead.
• Severe Facial / Nasal Trauma: Patients with active epistaxis, crushed facial bones, or open nasal fractures should not have their forehead and nose pressed against the bucky surface.
• Uncooperative or Bedridden Patients: Severely kyphotic elderly patients or pediatric patients who cannot hold the forehead-nose position should be positioned AP.
• Inferior Orbital Rim Evaluation (Limitation): Because the central ray is 0⁰, the dense petrous ridges completely superimpose over the orbits, obscuring the inferior orbital rims and orbital floor (a 15⁰ Caldwell or 37⁰ Waters view is needed for orbital floor/sinus assessment).

2. Technical Factors

3. Step-by-Step Patient & Part Positioning

• Patient Preparation: Remove all radiopaque accessories (hairpins, metallic clips, earrings, wigs, spectacles, dentures, hearing aids, and dental plates).
• General Stance:
  • Erect (Preferred): Seated or standing facing the vertical Bucky. This is more comfortable and prevents lateral body rotation.
  • Prone (Alternative): Patient lies prone on the radiographic table with arms resting comfortably near the shoulders for stabilization.
• Alignment of Reference Lines & Contact Points:
  1. Forehead & Nose Contact: Rest the patient’s forehead and tip of the nose firmly against the table or vertical Bucky surface.
  2. Orbitomeatal Line (OML): Adjust head flexion/extension so the OML is strictly perpendicular to the plane of the image receptor.
  3. Mid-Sagittal Plane (MSP): Align the MSP perpendicular to the midline of the grid/bucky. Stand directly behind the patient to check that the head is not rotated to the left or right.
  4. Interpupillary Line (IPL): Ensure the IPL is strictly parallel to the plane of the IR (no lateral head tilt).

4. Central Ray (CR) & Collimation

• CR Angle: 0⁰ (perpendicular to the image receptor and parallel to the OML).
• CR Alignment / Exit Point: Directed horizontally (or vertically if prone) to exit at the Glabella (or mid-nasion level).
• Collimation: Four-sided collimation adjusted to the outer skin margins of the skull vault (vertex superiorly, chin base inferiorly, and lateral outer calvarial borders).

5. Key Differences: 0° PA Baseline vs. 15° PA Caldwell vs. 0° AP

6. Radiographic Anatomy & Quality Evaluation Criteria