Brief Answer:
Extraocular muscle fibrosis versus sinus disease.

Detailed Answer:
Hi XXXXXXX
Thanks for writing in with your query.

Your question is very important and challenging. I would make my best attempt at helping you out.

I have read through your query in detail and would like to highlight some points related to your condition.

Mucocoeles (they fill up the sinus completely) are best imaged with a combination of CT (to assess bony changes) and MRI (to assess any extension into the orbit or intracranial compartment). Bone is always best imaged on CT and this is where CT scores over MRI.

Proceeding with CT features

The affected sinus is completely or partially opacified, and the margins expanded and usually thinned. Areas of complete bony resorption may be present resulting in bony defect and extension of the 'mass' into adjacent tissues. Peripheral calcification is sometimes seen. Following administration of contrast only peripheral enhancement (if any) is seen.

The content of the sinus is variable, depending on the degree of hydration, ranging from near water density, to hyperdense as secretion become increasingly thick and dehydrated.

Speaking of MRI features

MRI signal intensity is very variable and depends on the proportions of water, mucus and protein.

Please note that high signal is white and low signal is dark on MRI.

T1
water XXXXXXX content - low signal (most common)
protein XXXXXXX content - high signal

T2
water XXXXXXX content - high signal (most common)
protein XXXXXXX content - low signal

T1 C+ Contrast (Gd) - enhancement if present, only occurs at the periphery
DWI Diffusion weighted imaging - variable

It should be noted that colonisation with fungus can lead to very low signal on both T1 and T2 weighted sequences, mimicking a normal aerated sinus

Coming to your specific questions,

1. I also have some questions about the opacified ethmoidal cell. To my untrained eye, it appears to have gotten larger between the MRI and CT scans, and to develop extensions (in different slices) to the cells immediate above and below. But I'm suspicious of artifacts, and some of the images seem to have pretty poor resolution.

In my opinion, it remains the same in CT and MRI images. I acknowledge your perception but would like to attribute it to your untrained eye.


2. Do you think the lamina papryacia next to the opacified ethmoidal cell is intact? I can't see any bone on the CT - but I can't see bone in quite a number of places either. Is this a problem with the scan, or just inexperience?

Though there is no appreciable discontinuity, I would say that there is slight bulging of the lamina paprycia towards the orbit.

3. The "Thing" is barely visible on T1 without contrast, but nice and bright on T1 with contrast, and really bright on T2. Could a mucocele solidly enhance if it were as tiny as this (presumed) one?

By review of literature, mucocele shows peripheral enhancement. This appears more likely a mucous retention cyst as it is not filling up the entire sinus. Really bright on T2 is due to fluid presence.


Literature says

When the strabismus patient presents with an atypical history and examination, which could represent extraocular muscle fibrosis, it is worthwhile to investigate for possible sinus disease. Sinus treatment may improve alignment if the strabismus is of recent onset. Sinus disease management may also reduce the risk of strabismus recurrence after successful surgery. Regular stretching of the extraocular muscles to prevent shortening seemed to assist some patients when they began to notice recurrent diplopia. If unexpected fibrosis of the extraocular muscles is detected at surgery, sinus evaluation may still be of value to prevent strabismus recurrence.

In my closing remarks, the size of the problem is small and it appears to be relatively stable during the interval between the CT and MRI images. You clinical symptoms need attention nevertheless.

Hope I have been able to answer at least few of your queries.
Do write back in case of doubts.

Regards,
Dr.Vivek

---