The Comprehensive AOCMF Classification: Skull Base and Cranial Vault Fractures - Level 2 and 3 Tutorial

Abstract

The AOCMF Classification Group developed a hierarchical three-level craniomaxillofacial classification system with increasing level of complexity and details. The highest level 1 system distinguish four major anatomical units, including the mandible (code 91), midface (code 92), skull base (code 93), and cranial vault (code 94). This tutorial presents the level 2 and more detailed level 3 systems for the skull base and cranial vault units. The level 2 system describes fracture location outlining the topographic boundaries of the anatomic regions, considering in particular the endocranial and exocranial skull base surfaces. The endocranial skull base is divided into nine regions; a central skull base adjoining a left and right side are divided into the anterior, middle, and posterior skull base. The exocranial skull base surface and cranial vault are divided in regions defined by the names of the bones involved: frontal, parietal, temporal, sphenoid, and occipital bones. The level 3 system allows assessing fracture morphology described by the presence of fracture fragmentation, displacement, and bone loss. A documentation of associated intracranial diagnostic features is proposed. This tutorial is organized in a sequence of sections dealing with the description of the classification system with illustrations of the topographical skull base and cranial vault regions along with rules for fracture location and coding, a series of case examples with clinical imaging and a general discussion on the design of this classification.

Keywords: classification system; cranial vault; fracture classification; skull base.

Figure 1

Skull base, (A) endocranial and (B) exocranial surface. Tracing two sagittal lines parallel to the crista galli along the fronto-ethmoid rims, the endocranial surface of the skull base can be divided in a central and in two (right and left) parts. (A) The nine quadrants used for the anatomical location of the fractures. A, anterior skull base; C, central skull base; Ca, Central anterior skull base (Cribriform plate and etmoido-sphenoidal planum); Cm, Central middle skull base (sellar and parasellar comparments); Cp, Central posterior skull base (clivus); M, middle skull base; P, posterior skull base; a, anterior; m, middle; p, posterior. (B) F, frontal bone; O, occipital bone; P, parietal bone; S, sphenoid bone; T, temporal bone.

Figure 2

Cranial vault, (A) frontal and (B) lateral view. F: Frontal bone; P: Parietal bone; S: Sphenoid bone; T: Temporal bone; O: Occipital bone.

Figure 3

Examples of fractures and definitions. (A) Depressed fracture (displaced toward the brain) of the parietal bone. (B) Multiple fractures, depressed on the right frontal bone, displaced on the left frontal bone, with involvement and opacification of the frontal sinus bilaterally. (C) Transverse fracture line through the right petrous bone, another fracture line through the right apex petrosis, opacification of the left mastoid with fracture at the rostral rim. (D) Transverse maximum intensity projection (MIP) – reconstruction of the skull base with fragmented fracture of the right middle skull base fossa. (E): Nonfragmented fracture of the left parietal bone. (F) Curved MIP—reconstruction of the occipital bones with fragmented fracture, displaced but not depressed.

Figure 4

Examples of associated diagnostic features with skull base and cranial vault fractures. (A) Partial opacification in the sphenoid sinus with air–fluid level in computed tomographic imaging (representing possible the presence of blood or fluid). (B–D) Presence of intracranial air: single or multiple air-bubbles in the subdural spaces (arrows in B) or in the subarachnoid space (arrow in C); (D) pneumocephalus. (E–H) Intracranial mass lesions: (E) epidural hematoma in the left occipital region (arrowheads) with small mixed (epidural and subdural) hematoma in the right temporal region (arrows), (F) subdural hematoma of the right hemisphere (arrows) with extension along the falx (arrowhead), (G) intraventricular haematoma, (H) brain contusions.

Figure 5

Multiple cranial vault fractures. (A–F) Multiple cranial vault fractures. The right sided fractures involve the frontal and parietal vault with comminution and depression and extension inferiorly into the temporal cranial vault. Similarly, on the left, there is a linear parietal vault fracture that appears to continue into the temporal bone. (G) There is extension of these fractures into the left and right sphenoid bone. Imaging: Computed tomographic axial views. (H) Level 3 code: 93 S0.m.S0, 94 F1.P1.T0.m.T0.P0, This case example CMTR-93-94-001 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification.

Figure 6

Single skull base fracture extending the temporal cranial vault. (A–C) Fracture through the skull base involving the left temporal bone, (D–I) traversing the glenoid fossa, and extending into the temporal cranial vault. The fracture is linear, unbranched and non-fragmented. Imaging: Computed tomographic axial views. (I) Level 3 code: 93 m.T0, 94 m.T0, This case example CMTR-93-94-002 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification.

Figure 7

Right occipital and temporal cranial vault fracture extending into the right middle fossa skull base. (A–C) Right occipital cranial vault fracture extending inferiorly into the right temporal bone, (D–H) with extension across the right middle fossa skull base through the skull base portion of the right temporal bone. There does not appear to be any fragmentation. (D) A probable left sphenoid fracture may be noted as well. Imaging: Computed tomographic axial views. (I) Level 3 code: 93 T0.M0.m.S, 94 O0.m, This case example CMTR-93-94-003 is made available electronically for viewing using the AOCOIAC software at www.aocmf.org/classification.

Figure 8

Examples of cases in which the definitions of the first session of the classifications system caused disagreement. (A) According to the definitions of the first session, the fracture marked with the arrow was classified in different ways by the different participants of the pilot session: single branched or multiple and comminuted. The disagreement was solved in the following classification form, defining it single, ignoring the multiple cracks, because considered clinically irrelevant. (B) The fracture marked with the arrow was cause of controversies in the assignment to the definition “diastatic”. Considering the term “diastatic” clinically irrelevant and cause of disagreement, in the new form of the classification system that fracture was defined single fracture and displaced not depressed.