Soft-tissue injury, mainly including injury of the optic nerve, extraocular muscles, lacrimal glands, hemorrhage and hematoma, eyelid swelling, and gas accumulation within the orbital cavity and eyelid.

Optic nerve injury, divided into two kinds: (1) primary injury, including break, contusion, compression of optic nerve sheath, and adjacent cavity by hemorrhage, and (2) secondary injury, including optic nerve edema, compression of the vessel, or circular obstacle.

Extraocular muscle injuries, including break, block, contusion, scar contraction, and adhesion.

Lacrimal gland injury, including edema, hemorrhage, and prolapse.

Hemorrhage within the orbital cavity can distribute separately in the soft tissue or present as hematoma. Subperiosteum hematoma is defined as hematoma between the orbital periosteum and bone.

CT scan: CT scan is the first choice due to its convenience, fast speed, and high-density resolution.

MRI scans: Its soft tissue resolution is superior to CT scan. It can clearly reveal the injury of the optic nerve, extraocular muscles, and hematoma within the orbital cavity, better than CT scan. If the optic nerve injury is suspected, the MRI scan should be performed as soon as possible for the sake of treatment. Metal foreign bodies are contraindications.

Optic nerve injury: CT scan cannot show the optic nerve injury clearly. The injured optic nerve can only present as thickening, blurred edge or discontinuity (Fig. 3.8). Hemorrhage of the optic nerve sheath and adjacent cavity represents as increased density (Fig. 3.9). Coronal view can show annular higher density around the optic nerve. Besides the altered shape of the optic nerve, the MRI scan can show increased SI on T2WI of it, indicating contusion and edema. The SI around the optic nerve can be varied in different time points of the hemorrhage. Typical manifestation is high SI on T1WI and T2WI around the optic nerve.

Extraocular muscle injuries: CT and MRI scan can show the altered shape and location of the extraocular muscles, mainly including thickening, displacement, twist, or incarcerated to the fracture areas. (Fig. 3.8). When extraocular muscles are broken, the ruptured muscles are not always displayed on CT scan directly. Sometimes normal extraocular muscle is absent in the corresponding area, in this condition, the muscle break should be considered. (Fig. 3.10). MRI scan is superior to the CT scan due to the blurred fat space, spread edema, and hemorrhage. The lacerated and detached muscle tendon represented as mass can be showed clearly. The edema in the damage zone is present as (slightly) decreased SI on T1WI and high SI on T2WI. Hemorrhage within 2 weeks is present as high SI on both T1WI and T2WI, and its SI will be decreased as the time passes by. Scar with low SI and peripheral tissue adhesion will appear in the late stage of extraocular muscle injuries.

Lacrimal gland injury: CT images can show the increased volume of the lacrimal gland with blurred margin; increased density of the gland, which may due to hemorrhage; bone chips or foreign bodies in the gland; and the anterior and inferior displacement of the gland. MRI can show the edema (low SI on T1WI, high SI on T2WI) and hemorrhage (within 2 weeks, high SI on both T1WI and T2WI).

Hemorrhage in the orbital cavity: CT scan can show the blurred fat space retrospective to the eyeball, combined with patchy higher density (Fig. 3.11). Hematoma is present as oval or spindle-shaped, iso- or slightly high-density mass. Its MRI SI can be varied in different hemorrhage time points. Subperiosteum hematoma is present as spindle or flat mass along with the orbital wall, iso- or slightly high density, with clear border and without crossing the bone suture on the CT scan (Fig. 3.12). On the MRI, the SI variation of subperiosteum hematoma is same as that of hemorrhage: slightly low SI in the super acute and acute phase; slightly high SI in the subacute phase; and low SI on T1WI and high SI on T2WI in the chronic phase.