To describe a case of a CSF leak encountered during lateral orbital decompression surgery due to abnormally absent of part of lateral orbital roof.

The authors present a case of a 52 year old male who presented unilateral right proptosis in the setting of quiescent thyroid eye disease. The patient was distressed by the resulting facial asymmetry and was keen on rehabilitative surgery. He was offered a unilateral lateral wall decompression.
The chosen method of decompression was an anterior rim sparring technique.

An extended lateral canthotomy and exposure of the lateral orbital rim periosteum was performed and the periosteum reflected. Further periosteum reflection was performed intraorbitally. At that stage, a CSF leak was observed in the lateral wall – roof junction. A careful examination revealed a 1 cm x 7 mm bone defect in the orbital roof with direct exposure of the dura. No obvious dural tear was noted though a slow CSF leak appeared to be filtrating through.
The on-call neurosurgeon was contacted for advice. A Surgicel® haemostat was placed on the defect and the decompression aborted.

When retrospectively reviewing the orbital CT scan, we noted an abnormally attenuated orbital roof. This was not picked up preoperatively.
A literature search regarding abnormal orbital wall anatomy as well as complications related to lateral orbital decompression was performed. No similar presentations were found.