Orbital Muscle Enlargement: What if It’s Not Graves’ Disease?

Analysis of extraocular muscle volumes in idiopathic hypertrophic pachymeningitis patients

BACKGROUND

Idiopathic hypertrophic pachymeningitis (HP) is a rare chronic inflammatory condition without an identifiable cause characterized by fibrous thickening of the dura mater, which can involve the extraocular muscles (EOM).

OBJECTIVE

To evaluate volumetric changes of EOM in idiopathic HP patients compared with healthy controls (HC) and study the correlation with ocular motility disturbance.

MATERIALS AND METHOD

Twenty-two idiopathic HP patients diagnosed and underwent 3T MRI between 2017 to 2021 at Siriraj Hospital and 22 age- and sex-matched HC were included in this retrospective study. EOM was manually segmented from the T1W image using 3D Slicer software, and volume was calculated using FSL software. T-tests and Mann-Whitney U tests were used to compare EOM volumes between the idiopathic HP and control groups. Pearson's correlation coefficient was then used to assess the correlation between ocular motility and EOM enlargement.

RESULTS

In idiopathic HP patients, the average EOM volumes, including the medial rectus (p = 0.002 each), inferior rectus (right p = 0.08, left p < 0.01), inferior oblique (right p = 0.009, left p = 0.005), right lateral rectus (p = 0.005), right superior oblique (p = 0.004), and left superior rectus (p = 0.005) muscles, were significantly larger compared to those in HC, particularly in the left IR and both MR. However, there was no significant correlation between the enlargement of these 9 EOMs and the extraocular movement limitation.

CONCLUSION

In idiopathic HP patients, significantly larger EOM volumes were found compared to control subjects. This enlargement could be due to the diffuse infiltrative histopathology potentially involving microstructures in the EOM. Extraocular movement limitations may be related to cranial nerve involvement. However, the enlarged EOM volumes show no significant correlation with extraocular movement limitation.

Patterns of Extraocular Muscle Enlargement in Graves' Orbitopathy and Acromegaly

Purpose: Extraocular muscle (EOM) enlargement occurs in both acromegaly and Graves' disease, but the degree and pattern of enlargement have not been directly compared in these patient groups. This study investigated whether acromegaly and Graves' orbitopathy (GO) are associated with different patterns of EOM enlargement at the time of diagnosis. Study Design: Retrospective cohort. Methods: All new patients with a diagnosis of acromegaly or GO who presented to St Joseph's Health Care in London, Ontario, between January 1, 2015, and July 1, 2020, and who underwent computed tomography (CT) scanning with adequate orbital imaging were considered for inclusion. We included age- and sex-matched control patients with pituitary macroadenomas without thyroid or growth hormone abnormalities. Orbital CT scans were analyzed by a single neuroradiologist, who measured the maximum diameter and cross-sectional area of each EOM. The relative likelihood of involvement of each rectus EOM was analyzed separately using an analysis of variance test. Results: We included 16 patients with GO, 17 with acromegaly, and 18 controls. Ages (mean ± standard deviation) of groups were 55.6 ± 18.0, 50.2 ± 15.7, and 49.3 ± 14.0 years. The mean maximum diameter of EOMs in GO, acromegaly, and controls was inferior rectus (IR) = 4.77 ± 1.53, 4.66 ± 0.61, and 3.68 ± 0.61 mm; medial rectus (MR) = 5.35 ± 2.23, 4.84 ± 0.81, and 3.65 ± 0.42 mm; superior rectus (SR) = 4.94 ± 1.84, 4.88 ± 0.91, and 3.68 ± 0.61 mm; and lateral rectus (LR) = 3.91 ± 1.59, 4.55 ± 0.60, and 3.20 ± 0.43 mm. The IR, MR, and SR muscles were significantly larger in the GO group compared with controls (IR, p = 0.020; SR, p = 0.004; MR, p < 0.001; and LR, p = 0.166), and all four EOMs were larger in acromegaly compared with controls (IR, p = 0.039; SR, p = 0.006; MR, p = 0.006; and LR, p = 0.001). There was no significant difference between the GO and acromegaly groups (IR, p = 0.959; SR, p = 0.987; MR, p = 0.408; and LR, p = 0.250). Conclusions: GO and acromegaly groups demonstrated the enlargement of the IR, MR, and SR muscles when compared with controls. The GO group did not show significantly larger EOM sizes compared with the acromegaly group. In the GO group, the IR, MR, and SR were similarly affected and did not follow previously described patterns of enlargement in GO.

Practical Approach to Orbital Lesions by Anatomic Compartments

A wide range of pathologic conditions can originate in the orbit. While it is common to approach the differential diagnosis based on disease categories, such as neoplastic and inflammatory, segmenting the orbit into anatomic compartments can direct the radiologist toward the most common pathologic conditions for each manifestation and space. The orbit can be divided into intraconal, conal, and extraconal compartments. Additionally, the optic nerve sheath complex and lacrimal apparatus can be partitioned into separate compartments due to their unique functions and pathologic features. By using this anatomic approach, the authors review the most common pathologic conditions affecting the orbit and discuss clinical and imaging findings that can guide the differential diagnosis for lesions with similar appearances. Published under a CC BY 4.0 license. Supplemental material is available for this article.

Clinical and radiological characteristics of odontogenic orbital cellulitis

PURPOSE

To assess the radiological features and clinical outcomes of odontogenic orbital cellulitis.

METHOD

Multi-centre retrospective study of odontogenic orbital cellulitis. Primary outcomes assessed were causal organism(s), clinical signs, radiological findings, management and visual outcomes.

RESULTS

Four patients with odontogenic orbital cellulitis were identified for inclusion. There was an equal proportion of men and women with a mean age of 43 years (range 25-56 years). All patients presented with an orbital compartment syndrome, with visual acuity of counting fingers (n = 1, 25%), hand movements (n = 1, 25%) and no perception of light (n = 2, 50%). The organisms implicated were Streptococcus milleri (n = 3, 75%) and Streptococcus constellatus (n = 1, 25%). MRI findings showed a subperiosteal abscess was present in all cases, which was characterised radiologically as a T1-hyperintense, T2 minimally hyperintense collection with restricted diffusion and a low apparent diffusion coefficient signal. Final visual acuity ranged from 6/6 to no light perception. One patient required an orbital exenteration due to extensive necrosis with sepsis and systemic deterioration.

CONCLUSIONS

Odontogenic orbital cellulitis carries a serious risk of vision loss with a propensity to present with an orbital compartment syndrome secondary to Streptococcus species. Outcomes were highly variable, with two cases progressing to blindness of which one required an orbital exenteration.

Understanding Visual Disorders through Correlation of Clinical and Radiologic Findings

Patients presenting with visual disturbances often require a neuroimaging approach. The spectrum of visual disturbances includes three main categories: vision impairment, ocular motility dysfunction, and abnormal pupillary response. Decreased vision is usually due to an eye abnormality. However, it can also be related to other disorders affecting the visual pathway, from the retina to the occipital lobe. Ocular motility dysfunction may follow disorders of the cranial nerves responsible for eye movements (ie, oculomotor, trochlear, and abducens nerves); may be due to any abnormality that directly affects the extraocular muscles, such as tumor or inflammation; or may result from any orbital disease that can alter the anatomy or function of these muscles, leading to diplopia and strabismus. Given that pupillary response depends on the normal function of the sympathetic and parasympathetic pathways, an abnormality affecting these neuronal systems manifests, respectively, as pupillary miosis or mydriasis, with other related symptoms. In some cases, neuroimaging studies must complement the clinical ophthalmologic examination to better assess the anatomic and pathologic conditions that could explain the symptoms. US has a major role in the assessment of diseases of the eye and anterior orbit. CT is usually the first-line imaging modality because of its attainability, especially in trauma settings. MRI offers further information for inflammatory and tumoral cases. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

Clinical and imaging clues to the diagnosis and follow-up of ptosis and ophthalmoparesis

Ophthalmoparesis and ptosis can be caused by a wide range of rare or more prevalent diseases, several of which can be successfully treated. In this review, we provide clues to aid in the diagnosis of these diseases, based on the clinical symptoms, the involvement pattern and imaging features of extra-ocular muscles (EOM). Dysfunction of EOM including the levator palpebrae can be due to muscle weakness, anatomical restrictions or pathology affecting the innervation. A comprehensive literature review was performed to find clinical and imaging clues for the diagnosis and follow-up of ptosis and ophthalmoparesis. We used five patterns as a framework for differential diagnostic reasoning and for pattern recognition in symptomatology, EOM involvement and imaging results of individual patients. The five patterns were characterized by the presence of combination of ptosis, ophthalmoparesis, diplopia, pain, proptosis, nystagmus, extra-orbital symptoms, symmetry or fluctuations in symptoms. Each pattern was linked to anatomical locations and either hereditary or acquired diseases. Hereditary muscle diseases often lead to ophthalmoparesis without diplopia as a predominant feature, while in acquired eye muscle diseases ophthalmoparesis is often asymmetrical and can be accompanied by proptosis and pain. Fluctuation is a hallmark of an acquired synaptic disease like myasthenia gravis. Nystagmus is indicative of a central nervous system lesion. Second, specific EOM involvement patterns can also provide valuable diagnostic clues. In hereditary muscle diseases like chronic progressive external ophthalmoplegia (CPEO) and oculo-pharyngeal muscular dystrophy (OPMD) the superior rectus is often involved. In neuropathic disease, the pattern of involvement of the EOM can be linked to specific cranial nerves. In myasthenia gravis this pattern is variable within patients over time. Lastly, orbital imaging can aid in the diagnosis. Fat replacement of the EOM is commonly observed in hereditary myopathic diseases, such as CPEO. In contrast, inflammation and volume increases are often observed in acquired muscle diseases such as Graves' orbitopathy. In diseases with ophthalmoparesis and ptosis specific patterns of clinical symptoms, the EOM involvement pattern and orbital imaging provide valuable information for diagnosis and could prove valuable in the follow-up of disease progression and the understanding of disease pathophysiology.