Ossifying fibroma shows a mixture of well-demarcated mature lamellar bone along with woven bone.
The associated fibrous stroma is densely cellular. There is some osteoblastic rimming as well. Lesions with associated cementum are designated cemeno-ossifying fibroma.
In this second example, the stroma is very cellular (as seen here), but it can range quite a bit from this cellular to paucicellular.
Basophilic deposits (possibly cementum) are seen scattered within the stroma.
Ossifying fibromas (a.k.a. cemento-ossifying fibroma or cementifying fibroma) are benign neoplasms composed of spicules of woven bone lined by osteoblasts, surrounded by a cellular stroma (Thompson).
If cementum is present, then, the term cemento-ossifying fibroma or cementifying fibroma sometimes is used. The WHO (2005, Head and Neck tumors) stated that the mineralized component of ossifying fibromas may contain woven or lamellar bone, as well as basophilic deposits thought to be cementum. Cementum is defined as material covering the roots of teeth -- these deposits, if seen outside of this context, is virtually equivalent to bone. Therefore, distinguishing between cementum and bone is not clinically relevant (Barnes).
The key entity on the differential is fibrous dysplasia. It is important to separate these two entities as treatment and prognosis are quite different. Helpful distinguishing features include an infiltrative growth pattern in fibrous dysplasia (versus well-circumscribed in OF), immature woven bone without osteoblastic rimming in fibrous dysplasia (versus occasional lamellar bone and osteoblastic rimming in OF) and presence of activating missense mutation of the alpha subunit of a stimulatory G protein, GNAS, in fibrous dysplasia (Slootweg).
Ossifying fibromas affect females more frequently (F:M ratio of 5:1); the mandible is affected in 90% of cases. The mean age for presentation is approximately 30 years. The majority of cases are asymptomatic. Symptoms can include swelling, facial asymmetry and pain (Thompson).
Excellent. Complete excision is usually curative. A very small percentage of lesions recur locally.
A variant called juvenile psammomatoid ossifying fibroma occurs at a younger age with a greater tendency for recurrence and aggressive behavior.
Barnes L, Eveson JW, Reichart P, Sidransky D. WHO Classification: Pathology and Genetics, Head and Neck Tumors Lyons, France: IARC; 2005: 319.
Slootweg PJ. Lesions of the jaws. Histopathology 2009, 54, 401-418.
Thompson LDR, Wenig BM, eds. Diagnosis Pathology: Head and Neck. 1st Ed. Manitoba, Canada; Amirsys;2011; 6, 58-9.