Can you provide a diagram of the scalp block injection sites for frontal (supra‑orbital), temporal (pterional), parietal, and occipital craniotomies?

Scalp Block Injection Sites for Different Craniotomies

I cannot provide a visual diagram in this text-based format, but I will describe the precise anatomical injection sites and nerve targets for scalp blocks tailored to each craniotomy approach.

Anatomical Basis of Scalp Block

The scalp block requires anesthetizing multiple peripheral nerves that provide sensory innervation to different regions of the scalp 1, 2. The traditional approach involves blocking six key nerves bilaterally, though the specific nerves targeted depend on the surgical site.

The Six Primary Nerves:

1. Supraorbital nerve - exits through supraorbital foramen/notch
2. Supratrochlear nerve - medial to supraorbital nerve at medial orbital rim
3. Zygomaticotemporal nerve - lateral orbital rim area
4. Auriculotemporal nerve - anterior to ear at temporal region
5. Greater occipital nerve - posterior scalp, medial third of superior nuchal line
6. Lesser occipital nerve - posterior scalp, lateral to greater occipital nerve

Injection Sites by Craniotomy Type

Frontal (Supraorbital) Craniotomy

Primary nerves to block:

• Supraorbital nerve (bilateral)
• Supratrochlear nerve (bilateral)
• Zygomaticotemporal nerve (ipsilateral to incision)

Injection technique:

• Supraorbital: Inject at the supraorbital notch/foramen, palpable along superior orbital rim approximately 2.5 cm from midline
• Supratrochlear: Inject 1 cm medial to supraorbital injection site at medial orbital rim
• Zygomaticotemporal: Inject along lateral orbital rim, approximately 1 cm superior and lateral to lateral canthus

Temporal (Pterional) Craniotomy

Primary nerves to block:

• Auriculotemporal nerve (ipsilateral)
• Zygomaticotemporal nerve (ipsilateral)
• Supraorbital nerve (ipsilateral)
• Supratrochlear nerve (ipsilateral)

Injection technique:

• Auriculotemporal: Inject anterior to the tragus at the level of the external auditory meatus, approximately 1.5 cm anterior to ear cartilage 3
• Zygomaticotemporal: As described above
• Supraorbital/Supratrochlear: As described above
• Consider V3 block: For enhanced analgesia in temporal muscle area, ultrasound-guided injection in the infratemporal fossa between periosteum and lateral pterygoid muscle fascia may be considered 4

Parietal Craniotomy

Primary nerves to block:

• Auriculotemporal nerve (ipsilateral)
• Greater occipital nerve (ipsilateral)
• Lesser occipital nerve (ipsilateral)
• Supraorbital nerve (ipsilateral if anterior parietal)

Injection technique:

• Auriculotemporal: As described above
• Greater occipital: Inject at medial third of line between mastoid process and external occipital protuberance, approximately 2-3 cm lateral to midline at superior nuchal line
• Lesser occipital: Inject lateral to greater occipital nerve injection, approximately one-third distance from mastoid to external occipital protuberance

Occipital Craniotomy

Primary nerves to block:

• Greater occipital nerve (bilateral)
• Lesser occipital nerve (bilateral)
• Auriculotemporal nerve (bilateral if extending laterally)

Injection technique:

• Greater occipital: As described above, bilateral
• Lesser occipital: As described above, bilateral

Technical Considerations

Ultrasound Guidance

Ultrasound guidance should be used when available to reduce complications including intraneural injection, arterial puncture, and local anesthetic systemic toxicity 5. This is particularly important for:

• Auriculotemporal nerve blocks (to avoid superficial temporal artery)
• Supraorbital/supratrochlear blocks (to visualize vascular structures)
• Novel V3 blocks in infratemporal fossa 4

Local Anesthetic Dosing

• Volume per nerve: 3-5 mL typically sufficient for each nerve
• Total volume: Should not exceed maximum safe dose based on patient weight
• Concentration: 0.25-0.5% ropivacaine or bupivacaine commonly used
• Onset: 10-15 minutes for full effect

Critical Pitfalls to Avoid

1. Vascular injury: The superficial temporal artery courses very close to ear cartilage (mean 0.5-0.6 mm anterior to anterior edge) 3. Always aspirate before injection.

2. Facial nerve injury: Facial nerve branches course between galea and temporal fascia 6. Stay superficial to fascia when blocking auriculotemporal nerve.

3. Inadequate coverage: Scalp innervation has significant overlap. Block all nerves in the surgical field, not just those directly under incision 1, 2.

4. Local anesthetic systemic toxicity: The scalp is highly vascular. Use ultrasound guidance, aspirate frequently, and inject slowly 5.

Adjuncts and Modifications

For awake craniotomy, consider adding:

• Dexmedetomidine or propofol sedation
• Pin-site infiltration separately
• V3 block for temporal muscle manipulation 4

The interfascial plane between superficial and deep layers of temporal fascia provides optimal dissection plane and should guide injection depth for temporal approaches 6.