2 April 2009 – Case of the Week #142


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Thanks to Dr. Juan José Segura Fonseca, Pathology Department, Hospital San Juan de Dios, San Jose, Costa Rica, for contributing this case.  To contribute a Case of the Week, email NatPernick@Hotmail.com with the clinical history, your diagnosis and diagnostic microscopic images in JPG, GIF or TIFF format (send as attachments, we will shrink if necessary).  Please include any other images (gross, immunostains, etc.) that may be helpful or interesting.  We will write the discussion (unless you want to), list you as the contributor, and send you $35 (US dollars) by check or PayPal for your time after we send out the case.  Please only send cases with high quality images and a diagnosis that is somewhat unusual (or a case with unusual features).


Case of the Week #142


Clinical History


A 17 year old woman presented with difficulty swallowing and complained of a large foreign body sensation in her mouth for several months.  Physical examination revealed a bulging, rock-hard tumor covered with mucosa on the floor of her mouth.  Xray showed a large radioopaque tumor.  It was excised, and grossly was a multinodular mass of calcified tissue.


Xray: #1#2 (mass after excision)


Gross images: #1;  #2  

Micro images: #1;  #2#3;  #4


What is your diagnosis?




























Osseous choristoma of the floor of the mouth (osteoma)




The lesion is characterized by irregular mature bone trabeculae and fibrous connective tissue, with no osteoblastic activity and no atypia.  Vascular spaces reminiscent of Haversian channels are present.


A choristoma is a proliferation of tissues foreign to the site at which it is located.  Choristomas of mature bone (osseous choristomas) are rare in the soft tissue of the oral cavity.  They present as hard tumor-like masses in the tongue in about 85% of cases, usually in the posterior third (Indian J Pathol Microbiol 2009;52:86, Kaohsiung J Med Sci 1998;14:727, Gerodontology 2009;26:78) and less commonly at other sites, such as oral mucosa (Med Oral 2003;8:220), soft palate (Eur Arch Otorhinolaryngol 1990;247:264) and submandibular region (J Craniomaxillofac Surg 2006;34:57).  Only a few cases have been reported in the floor of the mouth.


Osseous choristomas have been found at all ages, the youngest apparently a 2 month old girl (J Pediatr Surg 1987;22:365).  They have a predilection for women (Med Oral Patol Oral Cir Bucal 2008;13:e627, Ear Nose Threat J 1998;77:316).


The differential diagnosis includes:


● heterotopic ossification (myositis ossificans) - typically occurs within muscle, and has more osteoblastic activity

● ossifying fibroma - does affect the craniofacial skeleton, but has a proliferation of round, polyhedral or spindly cells, not seen in this case

● dystrophic calcification - often found in old thrombi, hemartomas or keratin-filled cysts, but it does not resemble bone.


Surgical excision is the treatment of choice and is curative. Local recurrence is rare (Oral Surg Oral Med Oral Pathol 1991;72:337).




Nat Pernick, M.D., President

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