Introduction

Tolosa-Hunt Syndrome (THS) is a rare neurological disorder characterised by severe and unilateral pain in and around the orbital region (cavernous sinus),¹ as well as dysfunction in cranial nerves (mainly III, IV, and VI). Clinicians typically use MRI and CT scans to identify signs of the condition (any signs of inflammation within the cavernous sinus and adjacent structures for differential diagnosis). These imaging techniques not only aid early recognition of the condition but also guide clinicians to identify steps for appropriate management to treat symptoms and prevent complications. This article provides an overview of the role of such imaging techniques in identifying the relevant disease characteristics to confirm THS, distinguish it from other causes of cranial nerve deficits such as tumours or infections, and to inform treatment & care decisions 

Tolosa-Hunt syndrome

THS is a neurological condition characterised by pain experienced in the orbital or periorbital region, a symptom commonly first noted by patients. Alongside pain, some of the common symptoms that patients face is a condition called ophthalmoplegia (paralysis of eye muscles). This paralysis leads to symptoms such as ptosis (drooping of upper eyelid) and diplopia (double vision).² These clinical symptoms manifest due to inflammation of the cavernous sinus, a cavity consisting of various channels of venous blood supply, and where cranial nerves III (Oculomotor nerve controlling eye and eyelid movements), IV (Trochlear nerve controlling the superior oblique muscle helping with eye up-down movements) and VI (Abducens nerve controlling the lateral rectus muscle helping with outward eye movements) pass through.³

The pathophysiology of the THS is mainly attributed to inflammation in the cavernous sinus and surrounding structures, however the exact cause of the inflammation is unclear.⁴ Studies have often shown it to involve inflammatory and autoimmune processes, triggering the swelling. Some case reports have associated the inflammation with conditions such as vasculitis (inflammation of blood vessels).⁵ Inflammation levels often fluctuate, which affect the rate at which symptoms progress, highlighting the need for a comprehensive diagnosis and management plan.

Differential diagnosis of THS

Diagnosis of THS is a challenging process due to its shared similarity of symptoms with other conditions, such as tumours, infections and vascular conditions.

Tumours

Various tumours may lead to the compression of cranial nerves involved in eye movement. For instance, meningiomas⁶ (slow-growing tumours arising from the meninges – the protective layers of the brain) share common symptoms with THS – headache, eye pain and nerve palsies. Pituitary adenomas⁷ (tumours in the pituitary gland) also affect the cavernous sinus, causing similar deficits.

Infections

Infections affecting the areas in and surrounding the cavernous sinus such as shingles or thrombosis also cause similar symptoms such as the THS. A cavernous sinus thrombosis, which is a blood clot within the region, causes nerve dysfunction as it blocks blood flow to the area. Shingles (Herpes Zoster) is caused by the varicella-zoster virus which leads to rashes and affects the ophthalmic branch of the trigeminal nerve (Cranial Nerve V) and causes ptosis and diplopia.⁸

Vascular conditions

Conditions such as arteriovenous malformations (AVM) and aneurysm involves the blood vessels near the cavernous sinus region, compressing cranial nerves and leads to severe headaches.⁹

MRI and CT scans are thus essential for a differential diagnosis, in ruling out similar conditions. MRI is useful to distinguish tumours or infections, whereas CT scans help visualise bony structures surrounding the cavernous sinus region.¹⁰ 

Role of MRI in diagnosing Tolosa-Hunt syndrome

Magnetic Resonance Imaging (MRI) plays a critical role in diagnosing THS. One of the main characteristic features of THS is inflammation within the cavernous sinus, and the presence of soft tissue infiltration and enlargement of the cavernous sinus is a key observation that differentiates THS from other conditions with similar symptoms.

As MRI is non-invasive in nature, and can help differentiate soft tissues, it is one of the primary imaging modalities to assess and detect inflammatory changes in THS.

T1 and T2 weighted MRI provides great insight into the inflammatory processes in the cavernous sinus. On T1 imaging, visualization post administration of the contrast may reveal moderate levels of enhancement in the cavernous sinus. T2 weighted MRI may show abnormal signal intensity and swelling, characteristic of inflammation, providing a comprehensive assessment.

Contrast enhancement is also beneficial to identify inflammation around the cranial nerves, and subtleties in enhancement provide a depth of information on disease progression to inform treatment plans.¹¹

Two case studies describe the MRI findings in THS; the first¹² is of a 36-year-old male with no prior significant medical history, who presented with right-sided retro-orbital pain and diplopia. In conjunction with the symptoms, neurological examinations revealed impaired function in the 3rd and 4th cranial nerves and numbness in the ophthalmic division of the trigeminal nerve. MRI findings revealed a noticeable enhancement in the right cavernous sinus, through the superior orbital fissure and the orbital apex (anatomical structures that facilitate the passage of nerves and blood vessels around the eye). Serial MRI was also administered to monitor the progress of steroid therapy prescribed to the patient, and the MRI findings revealed improvements in the concerned areas, highlighting its effectiveness in monitoring treatment response.

Another case¹³ of a 70-year-old male with a history of hypertension and cataract surgery highlighted the role of MRI in differential diagnosis. The patient presented with vision loss and limited eye movements in the right eye, as well as headaches and facial numbness on the left side. Clinicians treating the patient considered the role of THS in this situation, which was triggered by the recent cataract surgery and an inflammatory pseudotumor. These findings were supported by a contrast MRI which showed a lesion in the left orbit, involving the extraocular muscles.

There are several advantages of MRI over other imaging modalities, and the high sensitivity to soft tissue contrast, aiding a detailed visualisation of the soft tissues and serial MRI scans facilitating monitoring of inflammation, which is an objective evaluation of the therapeutic effectiveness.

Role of CT in diagnosing Tolosa-Hunt syndrome

While MRI is the gold standard to aid the diagnosis of THS, Computed Tomography (CT) may help in ruling out other potential causes of conditions responsible for the patient’s symptoms to confirm the diagnosis of THS. A CT may be a readily available option to visualize structural abnormalities responsible for the symptoms. CT imaging may help visualize subtle signs of subtle asymmetry or enlargement of the cavernous sinus, suggesting the play of pathological causes. A CT may be more beneficial in identifying any changes in bones, which may occur if inflammation spreads to any adjacent structures, such as surrounding bony walls. In such cases, a CT may show bone erosion or destruction, which could be an important to distinguish feature to differentiate from any tumours, infections, traumatic features, or vascular malformations. However, this is only noticeable when THS becomes more pronounced, and is not of much utility for early detection.¹⁴

Another key indication for THS in CT is the loss of anatomical details within the Mechel’s Cave near the trigeminal nerve. As the cavernous sinus is inflamed, the area around becomes obscured, and cannot be picked up on the CT scan. Studies have also observed increased tissue tensity within the pre-pontine cistern (where roots of the cranial nerves are located) as a sign of inflammation.¹⁵

An advantage in using CT is its ready availability and speed, making it more accessible in hospitals for emergency settings, especially in assessing the potentiality for conditions such as tumours or haemorrhages. 

Summary

Tolosa-Hunt Syndrome is a rare neurological disorder characterised by unilateral headaches and deficits in controlled eye movements arising due to inflammation in the cavernous sinus. This condition primarily affects the cranial nerves responsible for controlling eye movements, leading to symptoms such as diplopia and ptosis.

Imaging modalities such as MRI and CT provide great clinical utility in diagnosing and assessing the severity of Tolosa-Hunt Syndrome in patients. Along with neurological examinations and a thorough medical history, MRI is extremely beneficial in visualising inflammation and the involvement of cranial nerves near the cavernous sinus, owing to high sensitivity in soft tissue contrast. Computed Tomography may be used as an additional modality to help clinicians rule out conditions causing similar symptoms, although are less effective in detecting early signs of inflammation and damage.

Early diagnosis of THS through CT and MRI modalities helps guide clinicians in prescribing and monitoring treatments, such as corticosteroids. Such treatments provide great relief, relieve symptoms, as well as provide clinical indicators to assess treatment response through MRI and CT modalities.