(I) Imaging of a patient with diplopia.
[4]
“Red flag signs” that require immediate imaging:
1] Acute cranial nerve palsy,
especially pupil-involving,
3rd nerve palsy with diplopia associated with thunderclap headache à Ruptured intracranial aneurysm.
2] Sudden onset proptosis with painful ophthalmoplegia and diplopia à Cavernous sinus thrombosis.
3] Severe headache,
papilledema,
lateral rectus palsy with diplopia in lateral gaze of the involved eye à false localizing sign of raised intracranial pressure.
4] History of trauma with binocular diplopia in any gaze à Extra ocular muscle entrapment vs intra cranial bleed.
5] Diplopia in pediatric population.
(II) Imaging Strategies: [5,
6]
The neuro ophthalmological relay pathway needs to be imaged using specific imaging strategies.
(Table 2)
(III) Case spectrum.
We encountered a varying spectrum of lesions that caused diplopia which were classified based on these discrete anatomic zones:
1. Supra nuclear:
§ Progressive Supranuclear Palsy [7]: Characterized by midbrain tegmentum atrophy,
downward gaze palsy ("surprised" look),
dysarthria,
parkinsonism and dementia.
Characteristics imaging findings include flattening or concavity of the normally convex superior profile of the midbrain (hummingbird sign),
dilation of the Sylvian aqueduct and relative increase in the length of interpeduncular fossa.
Midbrain: pons ratio - reduced area ratio on the midline sagittal plane to approximately 0.12 (normal ~ 0.24).
(Figure 8)
Differentials: Parkinsons disease,
Multi system atrophy (MSA) or Cortico-basal degeneration.
§ Parinaud's syndrome [8]: Also known as the dorsal midbrain syndrome,
is a supranuclear vertical gaze disturbance caused by compression of the tectal plate. It is characterised by a classic triad of findings which include upward gaze palsy,
often manifesting as diplopia,
pupillary light-near dissociation and convergence-retraction nystagmus.
Causes include pineal region lesions such as pineocytomas,
pineoblastomas,
pineal germinoma (Figure 9),
metastases,
tectal gliomas and posterior third ventricular arterio venous malformations (Figure 10).
2. Nuclear / internuclear:
§ Demyelinating lesions in multiple sclerosis (MS) can involve the brainstem causing ophthalmoplegia and nystagmus.
[9] McDonald MR criteria for MS is used to diagnose MS,
where there are lesions disseminated in time and space.
Demyelinating plaques are noted classically at the calloso-septal interface,
periventricular white matter (Dawson’s fingers) and cerebellum.
Active lesions will restrict on diffusion sequences and enhance on post contrast images.
(Figure 11)
§ Internuclear ophthalmoplegia due to involvement of the MLF by demyelination caused by Acute disseminated encephalomyelitis.
It is characterized by acute inflammation and demyelination of white matter after a recent (1-2 weeks prior) viral infection or vaccination.
Deep Gray matter (basal ganglia) and the spinal cord are also commonly involved.
(Figure 12)
§ Post-operative gliosis causing INO due to gliosis involving the MLF.
The patient is a post-operative case of posterior third ventricular arachnoid cyst.
3 year follow scan showed gliosis of the medial midbrain and pons (Figure 13)
§ Brain stem Cavernoma: are common intra axial vascular malformations.
MRI is the modality of choice,
demonstrating a characteristic “popcorn” appearance with a rim of signal loss due to hemosiderin,
which demonstrates prominent blooming on susceptibility weighted sequences. These are prone to haemorrhage.T1 and T2 hetero-intense lesions with variable enhancement patterns on post contrast imaging.
(Figure 14)
3. Infra nuclear:
ü Peribulbar cisterns (Interpeduncular cistern and Pre-pontine cistern):
§ TB meningitis [10] Commonly presents as pachymeningitis,
which enhances homogeneously and intensely,
sometimes nodular.
Exudates within the basal cisterns which appear bright on T2 FLAIR / T1 images.
Differentials are Sarcoidosis,
Fungal infections,
Metastasis.
(Figure 15)
§ Superior Cerebellar artery aneurysm: Posterior circulation aneurysms are rare (10 %).
Compression of the cisternal segment of the trochlear / oculomotor nerves are the common mechanism of diplopia.
(Figure 16)
§ Epidermoid [11]: They are commonly congenital (ectodermal inclusion during neural tube closure) or acquired (post surgical or post traumatic implantation).
Characteristically follow CSF signals in all sequences with heterogenous fluid signal suppression on T2 FLAIR images.
Classically have diffusion restriction which differentiates them from arachnoid cysts.
(Figure 17)
ü Petrous apex / tentorium cerebelli:
§ Chondrosarcoma: Lesions are epicentered on the right petro-clinoid fissure with matrix calcification,
infiltrating into right orbital apex. Stippled and/or amorphous calcified matrix are characteristic.
Variable signal intensity on T1 (due to haemorrhage or mucin) and hyper intense on T2 (fibrocartilaginous foci or areas of chondroid mineralization).
Differentials: Chordoma,
Meningioma or Metastasis.
(Figure 18)
§ Trigeminal nerve schwannoma: Usually hypo to isointense on T1 and hyper intense on T2,
relative to extraocular muscles and gray matter,
with heterogeneous contrast enhancement.
These lesions are usually cystic.
They can be “figure of 8” / “dumbell shape” in configuration as in our case.
(Figure 19)
ü Para sellar lesions [12]:
§ Cavernous sinus Haemangioma: Most common vascular tumour of the cavernous sinus.
Classically appear homogenously bright on T2 weighted images,
“ light bulb sign”.
They show progressive “filling in” of contrast on dynamic imaging.
Nonspecific intense homogeneous or heterogeneous contrast enhancement.
(Figure 20)
§ Meningioma in NF2: Most CS meningiomas arise from the lateral dural wall,
rarely within the sinus.
Usually hypo- to isointense with respect to gray matter in all sequences.
“Dural tail” frequently can be seen extending away from the edge of the tumour,
sometimes into the ipsilateral tentorium.
Differential: Schwannoma (Figure 21)
§ Internal carotid artery aneurysm from the cavernous segment of the ICA.
Usually are saccular in nature secondary to atherosclerosis.
They can have mass effect on the abducens nerve to cause lateral rectus palsy.
If not thrombosed,
flow voids and phse pulsation artifacts are characteristic for these lesions (Figure 22)
§ Cavernous sinus thrombosis: Usually secondary to paranasal sinus infection,
orbital cellulitis or midface infection.
Staphylococcus aureus is the most frequent causal organism.
T1 hyperintense cavernous sinus and diminished enhancement.
Abducens nerve is most commonly involved.
Important to rule out ipsilateral ICA thrombosis,
as noted in our case.
(Figure 23)
§ Carotico - cavernous fistula : Fistulas are direct (cavernous segment of the ICA and the cavernous sinus are in continuity) or indirect (feeders from meningeal branches from the carotid system- ICA/ ECA or both)
While dural or indirect fistulas often resolve spontaneously,
direct fistulas are high flow,
more symptomatic and usually require interventional treatment.
(Figure 24)
ü Orbital apex lesions [13]:
· En plaque meningioma: Diffuse plaque like dural involvement à usually with extracranial extension into calvarium,
orbit,
and soft tissues.
Significant osseous involvement.
Differentials are Intraosseous meningiomas (which have no intracranial extension) and Fibrous dysplasia (no peri osseous soft tissue component).
(Figure 25)
· Tolosa-hunt syndrome: Case of a 48-year-old female presenting with right sided painful ophthalmoplegia,
abducens nerve palsy and ptosis.
Workup was negative for Myasthenia.
She improved on oral corticosteroids on 2 year clinical follow up.
Asymmetric enlargement of ipsilateral cavernous sinus.
Enhancement is noted in the active phase.
It is a diagnosis of exclusion,
variant of an inflammatory pseudotumor.
Histology shows granulation tissue in the cavernous sinus at the orbital apex along the superior orbital fissure.
(Figure 26)
ü Orbital lesions:
§ Extra ocular muscle entrapment in orbital fractures: Post traumatic orbital wall fractures can lead to muscle herniation / entrapment,
most commonly in inferior orbital blowout fractures of the orbit.
Our case showed displaced orbital roof fracture with superior rectus entrapment.
(Figure 27)
§ Cavernous haemangioma: Recently classified as slow-flow venous malformations.
Gradual,
incomplete filling in of contrast.
Low-intensity septation or T2 hypo intense pseudo capsule.
Can have intra and extra- conal orbital components.
Differentials include veno -lymphatic malformation and hemangiopericytomas.
(Figure 28)
§ Inflammatory pseudotumor: Our case showed a right orbital apex IPT involving the medial rectus muscle,
with painful eye movements.
It is an infiltrative lesion.
Marked T2 hypo intensity is due to diffuse fibrotic change with collagen deposition.
Can extend to the dura,
skull base,
orbit and infratemporal fossa.
Clinically,
patients will have painful eye movements,
which differentiates it from lymphoma.
(Figure 29)