Painful sudden proptosis

Clinical History

On-call ophthalmology registrar referred a 67-year-old African male patient for sudden onset of painful right eye proptosis.
No significant past medical history, in particular, no Type 2 DM/trauma/goitre.
Right eye proptosis on examination.

CT head was performed to exclude the causes of acute onset painful proptosis - carotico-cavernous fistula/orbital cellulitis/cavernous sinus thrombosis/intra-orbital haemorrhage.

Imaging Findings

Contrast-enhanced and non-contrast CT showed extensive skull and mandible bone texture abnormality with occipital bone sparing. Bilateral zygomatic bones appeared lytic and expansile with soft tissue swelling more pronounced on the right causing retro-orbital and temporal lobe mass. Other skull bones (except occipital) also appeared lytic but with no soft tissue swelling. There was no evidence of cavernous sinus thrombosis, carotico-cavernous fistula or cellulitis.

MR imaging performed next morning was confirmatory showing low marrow signal on T1 and T2 weighted images with restricted diffusion in right zygomatic bone.

CT body performed after 2 days showed only a patchy increase in bone density elsewhere. No evidence of prostate enlargement or other primary malignancy. Axial and appendicular skeletons appeared lytic/sclerotic but without associated soft tissue masses.

Haemoglobinopathies screen was negative; PSA exceeded 1880 ng/ml. Hormonal therapy for metastatic prostatic carcinoma was therefore commenced without diagnostic biopsy. Follow-up CT after 5 days remained unchanged.

Discussion

Imaging was performed to exclude the known causes of painful unilateral proptosis. This case confirms metastasis as a cause of proptosis, although sudden onset unilateral proptosis is rarely caused by metastatic disease [1]. Similarly, painful proptosis due to metastasis is also unusual. In the author's opinion, as in sickle cell disease, the mechanism is probably bone infarction or ischaemia caused by bone marrow infiltration (by metastasis).

Final radiological impression for these appearances in an older adult male with no other significant past medical history was favoured to be metastatic disease, likely from a prostate primary - clinical correlation and blood PSA measurement was advised. PSA levels were > 1880 ng/ml which is highly specific for prostatic malignancy, the patient was commenced on hormonal therapy for metastatic prostatic carcinoma without a diagnostic biopsy. Follow up CT- after 5 days was unchanged.

Other differential diagnoses include myeloproliferative disorders such as mastocytosis and haemoglobinopathies but haematology, thalassemia and sickle cell screen were negative. Myeloma and fibrous dysplasia can also be considered in the differential for lytic bone lesions involving skull but over all clinical picture and investigations were not supportive of either.
An abscess could be another differential but unlikely, as the CT and MR pictures do not show any soft tissue swelling or periosteal reaction and the blood parameters were not suggestive of an infective aetiology.
The soft tissue is bilateral and very nearly symmetric which again does not fit with abscess in someone complaining of only right sided pain.

Fewer than 10% of prostatic metastases are lytic and fewer than 7% have atypical presentation. Only 2% of all skeletal metastases are localised to orbits and metastases from prostate accounts for approximately 3% of these.

Take home message:
Unusual presentations of common medical conditions are more common than unusual medical conditions. As this case illustrates, expansile lytic bilateral (almost symmetrical) zygomatic bone lesions with soft tissue masses are a very uncommon presentation of metastatic prostatic disease [2, 3] but prostate carcinoma is one of the most common causes of metastasis in an older male patient and should therefore be considered even if the radiological appearances are not entirely typical of it.

Differential Diagnosis List

Final Diagnosis

Unilateral proptosis due to prostatic metastasis

URL:	https://www.eurorad.org/case/10965
DOI:	10.1594/EURORAD/CASE.10965
ISSN:	1563-4086