## 3 Narrative Review
### Imaging Findings of Orbital Myositis  
Radiological findings in IOI typically demonstrate inflammatory changes across various intra-orbital structures, including the globe, lacimal glands, extraocular muscles (EOMs), orbital fat, and optic nerve [14]. Orbital myositis is a broad term referring to the inflammation of the EOMs and encompasses systemic inflammatory, autoimmune, and infectious diseases, as well as drug reactions, post-streptococcal pharyngeal infection, and parameoplastic immune phenomena, as potential causes. IOM, within this spectrum, represents a distinct entity and is the most common form [6]. IOM is characterized by an acute onset of a symptomatic triad--orbital pain, diplopia, and eyelid or conjunctival swelling or redness. CT scans generally do not offer sufficient detail to distinguish idiopathic orbital inflammation from other orbital mass lesions, often revealing non-specific masses within the orbit that can vary in size, shape, and location. Common imaging findings in CT or MRI typically reveal a homogeneous, fusiform enlargement of the muscle belly with enhancement, frequently accompanied by the involvement of the anterior muscle tendon. In acute cases, the affected muscle is usually well defined; however, in chronic cases, especially those involving multiple muscles or associated systemic diseases, the borders tend to be less distinct, with inflammatory processes extending into the adjacent orbital fat [9]. In chronic cases, extraocular muscles typically appear hypointense on both T1- and T2-weighted MRI images. A hyperintense signal on T2-weighted sequences is indicative of increased intra- and extracellular fluid, often linked to inflammatory or neoplastic processes, while hypointensity may suggest fibrosis [15]. The administration of a gadolinium contrast during MRI further enhances the ability to detect areas of inflammation, infiltration, or venous congestion, which appear as regions of enhancement. In contrast, malignant tumors often exhibit heterogeneous signal patterns [14]. The use of fat suppression techniques during MRI is particularly valuable, as it helps to clearly delineate optic nerve sheath involvement and inflammatory changes within the orbit [15]. The typical features of IOM on CT or MRI are homogeneous fusiform enlargement with enhancement, often associated with the involvement of the anterior tendon. Cylindrical enlargement may also be present. In acute cases, the muscle contours are well defined, whereas in chronic cases, the muscle contours are blurred due to the involvement of the periporbital fat [9]. [PERSON] et al. conducted a multicenter retrospective study involving 24 patients (mean age: 44.4 \(\pm\) 17.8 years; 11 males) evaluated from 2011 to 2022. Among them, one case (4.2%) was pediatric (17 years old), and six patients experienced recurrence. It was found that active IOM was characterized by a fusiform enlargement of the EOM, elevated T2 signal intensity, and contrast enhancement. The average maximum diameters of the EOM ranged from 4.6 to 7.7 mm, with an enlargement ratio of 1.4 to 2.2. A total of 18 patients (75%) had the involvement of a single EOM, most commonly the medial rectus. Other affected ipsilateral structures included focal orbital fat (16 out of 24 patients, or 66.7%) and the lacimal gland (8 out of 24 patients, or 33.3%). Changes in the contralateral EOM and/or lacimal gland were noted in seven patients (29.2%). Additionally, patients with recurrence were more likely to experience ongoing recurrent episodes (\(p\) = 0.003) [16]. In five cases of orbital myositis reported by [PERSON] et al., orbital MRI revealed the enlargement and contrast enhancement of the affected muscles in all patients [17]. The same findings were observed in another five cases reported by [PERSON], where contrast-enhanced orbital MRI most effectively revealed swelling, signal hyperintensity, and the enhancement of isolated extraocular muscles [18]. A few years later, in 2015, [PERSON] et al.