Middle cranial fossa

• Abbreviation
• A., artery; Ac., acoustic; Cav., cavernous; CN, cranial nerve; Cond., condyle; Eust., eustachian; Ext., external; Gr., greater; Lat., lateral; Less., lesser; Lig., ligament; M., muscle; Mandib., mandibular; Mast., mastoid; Max., maxillary; N., nerve; Ophth., ophthalmic; Pet., petrosal; Petroling., petrolingual; Petrosphen., petrosphenoid; Plex., plexus; Pteryg., pterygoid; Seg., segment; Semicirc., semicircular; Temp., temporalis; Tymp., tympani

• Anteriorly:
• Separated from the anterior cranial fossa by the sphenoid ridge and the chiasmatic sulcus.

• Posteriorly:
• Separated from the posterior cranial fossa by the petrous ridges (petrous apices) and the dorsum sellae and posterior clinoid processes.

• Floor Composition:
• The upper surface of the middle cranial base floor is formed anteriorly by the greater sphenoid wing and the posterior two-thirds of the sphenoid body.
• The greater sphenoid wing forms the largest part of the endocranial surface.
• The posterior part of the floor is formed by the upper surface of the temporal bone. The squamosal and petrosal parts of the temporal bone complete this surface.

• The basal surface of the temporal lobe rests directly on the middle fossa floor.

• The medial part of the middle cranial base contains the sellar and parasellar region, including the pituitary gland and the cavernous sinus, which sits on the lateral aspect of the body of the sphenoid bone.

• The middle incisural space (containing the crural and ambient cisterns) is situated lateral to the midbrain/upper pons, adjacent to the temporal horn of the lateral ventricle.

• Superior Orbital Fissure (SOF):
• Located between the lesser and greater sphenoid wings. It transmits the oculomotor (CN III), trochlear (CN IV), ophthalmic (CN V1), and abducens (CN VI) nerves, a recurrent meningeal artery, and the superior and inferior ophthalmic veins. The SOF provides communication between the orbit and the MCF.

• Foramen Rotundum:
• Transmits the maxillary nerve (CN V2), located in the greater wing of the sphenoid.

• Foramen Ovale:
• Transmits the mandibular nerve (CN V3), located in the greater wing of the sphenoid.

• Foramen Spinosum:
• Transmits the middle meningeal artery (MMA).

• Carotid Canal:
• Provides passage for the internal carotid artery (ICA) and carotid sympathetic nerves. The petrous segment of the ICA is contained within the temporal bone below the MCF floor.

• Meckel's Cave/Trigeminal Impression:
• Located on the upper surface of the petrous bone where the trigeminal root enters the middle fossa and the semilunar ganglion sits. The dura covering the MCF forms the superolateral boundary of Meckel's cave.

• Arcuate Eminence:
• A prominence on the petrous bone surface that approximates the location of the superior semicircular canal.

• Petrosal Nerves:
• The upper surface of the petrous bone (part of the MCF floor) is grooved along the course of the greater and lesser petrosal nerves. The greater petrosal nerve courses above the petrous ICA; the lesser petrosal nerve courses anterior to the greater petrosal nerve.

• Surgical Access Routes:
• Frontotemporal (Pterional) Approach: Used widely, often requires removing the sphenoid ridge and extending bone removal downward to access the MCF floor.
• Subtemporal Approach: Involves elevating the temporal lobe from the MCF floor to access the cisterns around the tentorial incisura.
• Middle Fossa Approach: A temporal craniotomy followed by extradural elevation of the dura from the MCF floor is used to access the internal acoustic meatus, primarily for small tumors where hearing preservation is sought.
• Anterior Petrosectomy/Extended Middle Fossa Approach: Resection of the anterior petrous pyramid (part of the MCF floor) is employed to access the upper clivus, anterior surface of the pons, and adjacent cavernous sinus.
• Expanded Endoscopic Approaches: Lateral extensions of the sphenoid sinus below the MCF floor facilitate expanded endoscopic endonasal access to the cavernous sinus, MCF, and Meckel’s cave.

• Vascular and Neural Structures at Risk:
• Facial Nerve and Vessels: The petrosal artery, a branch of the Middle Meningeal Artery (MMA), supplies the facial nerve and geniculate ganglion, crossing the MCF floor. It is at risk during dura elevation, drilling of the floor, or embolization of the MMA, and damage may lead to facial nerve deficits.
• Dehiscence Risk: The bone covering the geniculate ganglion (gained access in the middle fossa approach) may be partially or totally absent in 15% to 16% of specimens, exposing the facial nerve to injury during dura elevation. Similarly, the petrous carotid artery may be exposed without a covering of bone in the MCF floor.
• Cochlea Injury: The cochlea lies immediately below the MCF floor, close to the petrous carotid artery, and can be injured during approaches that require drilling in this area (e.g., anterior petrosectomy).
• Trigeminal Nerve Compression: The initial intracranial portion of the MMA, entering through the foramen spinosum, can be elevated and stretched by lesions arising at the cranial base.
• Internal Capsule Proximity: Foramen of Monro is located deep to a point approximately 2 cm above the pterion. The genu of the internal capsule touches the ventricular wall lateral to the foramen of Monro; care is needed during retraction in this area to avoid hemiplegia.

• Surgical Landmarks (Middle Fossa Triangles): Specific triangular areas are defined by cranial nerves on the MCF floor:
• Anteromedial Middle Fossa Triangle: Situated between the ophthalmic (V1) and maxillary (V2) nerves; removing bone here opens into the sphenoid sinus.
• Posteromedial Middle Fossa Triangle (Kawase's Triangle): Located between the greater petrosal nerve and the lateral edge of the trigeminal nerve; removing bone in this area exposes the lateral edge of the clivus.
• Posterolateral Middle Fossa Triangle (Glasscock's Triangle): Located between the mandibular nerve (V3) and the greater petrosal nerve, containing the foramen spinosum; opening the floor here exposes the infratemporal fossa.

graph TD
  A["Test1"] --> B["Test2"]

graph LR
    A[Memory] --> B[Short-term memory]
    A --> C[Long-term memory]
    A --> D[Sensory memory]
    D --> E[Haptic memory]
    D --> F[Echoic memory]
    D --> G[Iconic memory]
    B --> H[Working memory]
    C --> I[Declarative/Explicit memory]
    C --> J[Non-declarative/Implicit memory]
    I --> K[Episodic memory]
    K --> K1[Autobiographical episodic memory]
    K --> K2[Experimental episodic memory]
    K2 --> K3[Flashbulb memory]
    I --> L[Semantic memory]
    J --> M[Procedural memory]
    J --> N[Associative memory]
    J --> O[Non-associative memory]
    J --> P[Priming]

    %% Define classes with specific styles
    classDef memory fill:Black,stroke:#333,stroke-width:2px,font-size:30;
    classDef SensoryMemory fill:Green,stroke:#333,stroke-width:2px;
    classDef shortTerm fill:#ff6161,stroke:#333,stroke-width:2px;
    classDef longTerm fill:#000080,stroke:#333,stroke-width:2px; 
    classDef declarative fill:#00BFFF,stroke:#333,stroke-width:2px;
    classDef nonDeclarative fill:#4682B4,stroke:#333,stroke-width:2px;

    %% Apply classes to nodes
    class A memory;
    class D,E,F,G SensoryMemory;
    class B,H shortTerm;
    class I,K,K1,K2,K3,L declarative;
    class C longTerm;
    class J,M,N,O,P nonDeclarative;