It was a regular day at the clinic for me on a Monday morning. I had just finished my morning surgery list and came down to the clinic to see patients. The first patient on the clinic list was a 10 year old kid who gave a history of hitting a stationary tractor while riding on his cycle about 15 days ago. The tractor’s back had made contact with his forehead. He had fallen unconscious and was taken to a local hospital. There he was examined by an emergency physician, he noted Bilateral ecchymoses and lid oedema (classical Raccoon eyes or Black eye sign of a scalp injury). The physician had ordered a CT scan which did not reveal any facial fracture or intracranial injury. Thus, he was given conservative treatment and discharged.
While the oedema and ecchymoses reduced, the protrusion of the left eye was increasing slowly with development of diplopia and reduced vision in the left eye. When they went back to the physician, he consoled them that everything will get alright in a few days. However, luckily for the boy, the parents did not buy this reasoning and came to Bangalore to get it seen by an ophthalmologist. They landed up in the hospital I was operating that day. As I came down to the clinic, my colleague told me to see a patient urgently.
When I saw the child. He had a non-axial proptosis with the left eye down and out. This explained the diplopia. He also had diminution of vision and a left sided RAPD (Relative Afferent Pupillary Defect) in the left eye indicating optic nerve compromise. My mind was ticking why he was having a proptosis and why nothing was picked up at the time of injury. I looked at the 15 day old CT scans and nothing out of the ordinary was seen.
The child at presentation had his left eye down and out with non-axial proptosis
I didn’t have a lot of time and had to think on my feet. I immediately told the parents to get the child admitted to a teaching hospital I work in, instructing my residents to get a Repeat CT scan done and get the blood work and evaluation done for general anaesthesia. The CT scan was done on an emergency basis. I also asked the Neurosurgeon to be on standby while I rushed to the hospital.
The CT showed a well defined mass in the supero-medial quadrant of the left orbit pushing the intraorbital contents outward and downwards. The mass was putting pressure on the optic nerve. All this explained the proptosis, diplopia and reducing vision.
Diagnosis was simple once the CT images arrived.
The classical dome shaped mass limited by the orbital wall periosteum was either a sub-periosteal hematoma (SPH) or abscess. The diagnosis was veering more towards the former as there were no systemic signs of an infection and an isolated primary orbital abscess in an immuno-competent individual is very rare.
However the clincher in radiological diagnosis of a lesion is in the Hounsfield Units (HU). Hounsfield units (HU) represent a scale of radiation attenuation values of tissues. The number assigned is called the Hounsfield number. This particular number usually ranges from -1000 to +1000 HU or above. A higher number indicated a greater attenuation of X-rays thus meaning higher tissue density. Each tissue has a somewhat signature HU range. A dermoid cyst for example which is filled with fat has a HU value between zero and -100 while air can have a HU value around -1000. Calcification +100 and cortical bone +300 and above. A hematoma has a HU value between +50 to +80.
I called the Radiologist friend who was on his way home. I convinced him to return back to hospital to provide me the HU value for the collection causing the proptosis. Once he returned back to his console, he confirmed that the lesion has a HU value of +63 and sent me the confirmation with a photo.
While the radiologist was checking the HU values, my residents mobilised the child for surgery under general anaesthesia. I was waiting in the OT for the Radiologist’s confirmation before I went in though I was convinced it was a SPH. I went in with a wide bore syringe to access the sub-periosteal space where the clotted blood was there and suctioned it out.
There was on table resolution of proptosis and by next day the vision had improved and the RAPD had reversed.
It was an absolute success! Yay! The boy’s left eye was saved!
Check out the time-lapse video of the procedure on my instagram handle.
If you are doctor and you’ve read thus far, you must be wondering why the initial CT scan had not picked up the SPH. The answer is in the slice thickness ordered. Most CT scan centres in India acquire CT scans at 5mm slice thickness to save time and radiographic films- thus cost per scan. The orbit’s length in an adult is around 40-50mm. In a child, if you order a CT scan with 5mm thick slice thickness there are going to be very few slices acquired of the orbit. So through averaging, it sometimes totally misses the orbital lesion or even a fracture. This has happened to my patients enough times for me to re-order scans to many of my paediatric patients whenever the clinical details don’t correlate with radiological imaging. In this case, my residents knew the protocol that I want the CT scans ordered- 1mm cuts, Axial, Coronal, Sagittal and 3D reconstruction, Zero Gantry!
So the lessons from the case
- When ordering CT scans for the face order 1-2mm slice thickness, so that you do not miss the fractures and the lesions. EDUCATE everyone else who orders Face scans!!
- Do not hesitate to re-order scans with the correct protocol if your clinical findings are not correlating with the imaging.
- Do not waste time intellectually trying to guess the diagnosis. Harness the different specialities in your reach to get the diagnosis as soon as possible while you work to take action simultaneously– again using the resources at your disposal. I did this by harnessing my Radiologist friend, the teaching hospital, it’s residents and the Neurosurgeon, even though the Neurosurgeon was not needed in the end.
While going home that evening, I reflected on how much technology had advanced that surgeons like me get to perform apparent everyday miracles like this while confidently knowing what it is that we are going after. Couldn’t help but remember Arthur C Clark’s third law:
“Any sufficiently advanced piece of technology is indistinguishable from magic.”