Faecal Occult Blood Test

Case of the Month (Emma Scurrell March 2011)

An orbital meningioma in a 10 year old female Bull Mastiff 

The following are pictures of the gross and histopathological specimens taken from the exenterated orbit of 10-year old female Bull Mastiff which presented with exophthalmos, protrusion of the third eyelid and blindness in the left eye. Ophthalmic evaluation revealed a swollen optic nerve head and indentation of the posterior sclera. An MRI scan confirmed the presence of an orbital mass and orbital exenteration was performed via an orbitotomy.


 Fig 1. Gross section of the globe and orbital mass. The orbital mass is cone-shaped and surrounds the optic nerve. The distal end of the optic nerve is marked with a red arrow. 


Fig 2. H&E section of the orbital mass, which is composed of neoplastic epithelioid meningothelial (arachnoid cap) cells.

 

Fig 3. H&E section of the orbital mass revealing osseous and chondroid metaplasia which is a common finding in these neoplasms.






Final Diagnosis

Canine orbital meningioma

Discussion

This is a slow-growing neoplasm which arises from the extradural arachnoid cap cells and typically surrounds the optic nerve to form a cone-shaped orbital mass. The neoplastic cells infiltrate the surrounding orbital fat, skeletal muscle and, in some cases, the posterior globe itself.  Complete resection can be challenging and any remaining neoplastic tissue will result in local recurrence and/or extension into the optic foramen, optic chiasm or brain.  Metastasis is rare. The histopathological pattern is meningotheliomatous whereby neoplastic cells are most often epithelial-like in appearance and hence the tumour must not be confused with a carcinoma.  An additional unusual but common finding in these tumours is osseous and chondroid metaplasia, a feature which can be diagnostically useful. 

Previous Monthly Cases

Hypertensive Retinopathy January 2010
FIP in a cat - uncommon presentation February 2010
Phaeohyphomycosis    March 2010 
Scleral Rupture April 2010
Canine and feline epulides May 2010
Erythema multiforme in a labrador retreiver June 2010
Keloidal fibrosarcoma in a labrador retreiver July 2010
Cutaneous epitheliotropic lymphoma  August 2010 
Benign cutaneous histiocytoma  September 2010 
Iridociliary adenoma October 2010
Proliferative thrombovascular necrosis of the pinnae November 2010
Signet-ring cell carcinoma in the stomach of a dog December 2010
Cutaneous infiltrative lipoma in a labrador January 2011

Tonsillar squamous cell carcinoma February 2011





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Faecal Occult Blood Test