Indications and approach planning
The main goal of the operation is to obtain wide temporary access to brain structures and then restore the anatomical integrity of the cranial vault. Most often, the approach is formed in the frontotemporoparietal region.
The procedure is frequently performed for emergency life-saving indications in neurosurgery. The main reasons include strokes, removal of intracranial hematomas, foci of inflammation and tumors, as well as the need for urgent arrest of bleeding from the trunk or posterior branch of the middle meningeal artery (a. meningea media).
For precise planning, surgeons use the Krönlein scheme. The soft tissue incision is marked in a horseshoe shape, with the base of the flap directed downwards toward the zygomatic arch. This is critically important to maintain adequate blood supply, which is provided by the vessels of this region (usually the superficial temporal artery). The length of the base must be at least 6–7 cm, and its edges should be 1 cm away from the orbital margin and the tragus of the auricle.
Soft tissue flap formation
The operation involves separate tissue dissection. First, a musculocutaneous-aponeurotic flap is formed. The surgeon incises the skin, subcutaneous adipose tissue, and the galea aponeurotica in a continuous line. An immutable rule applies here: the skin incision must be wider than the planned bone incision. If the soft tissue suture lines and the bone saw line coincide at the same level, the risk of postoperative infection and cerebrospinal fluid leakage (liquorrhea) will increase sharply.
After skin incision, the deep layers are exposed: the temporal muscle (m. temporalis), fascia, and periosteum (periosteum). The temporal muscle is gently separated along its fibers in the upper sections and transected transversely in the lower areas using an electrosurgical knife or scalpel. The formed soft tissue flap is turned downwards and carefully placed on gauze pads pre-soaked in a 3% hydrogen peroxide solution.
Bone trepanation and flap reflection
At the next stage, the osteoperiosteal flap is outlined. The periosteum is incised in an arced shape, stepping back exactly 1 cm from the edges of the previously made skin incision, and reflected in both directions, creating a smooth "pathway" as wide as the burr diameter.
5–7 burr holes are placed along the perimeter of the marked contour. The instrument must be used extremely carefully: the temporal bone in this zone is thin, and there is a real risk of the burr "plunging" into the brain tissue.
After creating the holes, the dura mater (dura mater) is gently detached from the inner bone plate. A Gigli wire saw is used to connect the holes. To avoid damaging the brain membrane, a metal Polenov guide is passed through the burr holes between the bone and the dura mater. Its thickened end bluntly dissects the tissues, and a special hook engages the saw loop, which is then pulled out.
Sawing of the bone bridges is performed strictly at an 45° angle to the skull surface. Due to this, the outer area of the bone flap turns out larger than the inner one — when closing the wound, it fits into the defect like a plug without sinking inwards.
The lower bone bridge is not sawed through. Two elevators are inserted into adjacent holes and the base is fractured. If the bone does not yield, it is nibbled away with Dahlgren rongeurs. The flap is turned back, strictly preserving its connection with the periosteum to ensure blood supply.
Intracranial stage and closure
In the open wound, the surgeon encounters a tense dura mater. Depending on the surgical task, it is incised linearly or a cruciate (horseshoe-shaped) incision is made, carefully taking into account the topography of venous and arterial vessels. The edges of the membrane are secured with stay sutures for inspection of the subdural space.
In case of bleeding from a. meningea media, the vessel is transfixed with small round needles and securely ligated with fine silk ties. The cavity is washed with a jet of isotonic sodium chloride solution, removing the hematoma and blood clots.
After completing the main stage, the bone flap is returned to its place, positioning it into the formed bed. The operation ends with meticulous hemostasis and careful layered closure of the wound.
Briefly: answers to topical questions
What lines and anatomical landmarks are used to construct the Krönlein scheme?
To construct the Krönlein scheme, two horizontal, three vertical, and one sagittal lines are used, drawn through the bony landmarks of the skull.
- Median sagittal line — from the glabella (glabella) to the external occipital protuberance (protuberantia occipitalis externa).
- Main lower horizontal line — through the infraorbital margin and the upper edge of the external acoustic meatus.
- Upper horizontal line — through the supraorbital margin parallel to the lower one.
- Anterior vertical line — through the middle of the zygomatic arch.
- Middle vertical line — through the middle of the mandibular condylar process.
- Posterior vertical line — through the posterior border of the mastoid process base.
What surgical instruments are used to form holes and saw the bone during trepanation?
Special neurosurgical and bone instrumentation is used to form burr holes and saw the bone during trepanation.
- Trephines and burrs — manual or electric trephines with spear-shaped, cone-shaped, and spherical (round) burrs for drilling holes.
- Gigli saw — a wire saw for cutting through the bone bridges between the holes.
- Polenov guide — a metal plate for passing the Gigli saw between the bone and the dura mater.
- Dahlgren rongeurs — for nibbling the base of the flap or dividing bone segments.
Perforators, drills, and gimlets can also be used.
What methods are used for surgical arrest of bleeding from a damaged middle meningeal artery?
Surgical arrest of bleeding from a damaged middle meningeal artery is performed by its ligation.
- Ligation of the artery ends — the main method in which the trunk or branches of the middle meningeal artery are transfixed using small round needles.
- Ligation — tying off the vessel with fine silk ligatures.
To access the trunk and posterior branch of the artery for their ligation, an osteoplastic craniotomy is performed with the formation of a horseshoe-shaped flap based at the zygomatic arch.
Through which anatomical opening does the middle meningeal artery enter the cranial cavity?
The middle meningeal artery enters the cranial cavity through the foramen spinosum.
- Foramen spinosum (foramen spinosum) — an anatomical structure through which the middle meningeal artery (a. meningea media) passes, along with its accompanying vein and the meningeal branch of the mandibular nerve.
The artery heads into this opening from the first (maxillary) segment of the maxillary artery (a. maxillaris).
How does osteoplastic craniotomy differ from decompressive (resection) craniotomy?
Osteoplastic craniotomy involves sawing out a bone flap on a nourishing pedicle with its subsequent return to its place and is used to access the cranial cavity while preserving the bone flap to close the defect. Resection craniotomy is allowed when a tumor is localized in the posterior cranial fossa or in severe intracranial hypertension with the threat of herniation; decompressive craniotomy is used for brain compression.
The "Different Levels" rule: the soft tissue suture line must never coincide with the bone saw line. This is the main condition for preventing infection and CSF leakage.
Class and exam questions
Why cut the bone at a 45-degree angle?
With such a bevel cut, the outer surface of the flap becomes larger than the inner one. This forms a distinctive bony ledge that reliably prevents the flap from collapsing into the cranial cavity postoperatively.
How to protect the meninges while using a Gigli saw?
For this purpose, the Polenov guide is used. The thickened end of the metal plate is inserted between the bone and the dura mater, isolating the tissues from the damaging action of the Gigli wire saw.
Why should the base of the bone flap be fractured rather than completely sawed through?
Fracturing the lower bone bridge allows preserving the continuity of the nourishing periosteal pedicle. It is through this pedicle that the blood supply to the bone is maintained, which is necessary for its engraftment.
What else to study on this topic
- Krönlein's scheme for the projection of intracranial formations
- Topography of the middle meningeal artery and technique of its ligation
- Blood supply of the scalp-aponeurotic flap of the temporal region
- Methods of hemostasis in damage to arachnoid granulations and dural venous sinuses
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