COM May 2012 Diagnosis

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The radiographic findings of a unilocular radiolucency with scalloped border are typical of an odontogenic keratocyst (OKC). The location and the age of this patient are also supportive of this condition and for that reason; OKC should be considered and placed high on the differential diagnosis list. However the described expansion of the bone is unlike the behavior of an OKC but expansion has been described in larger OKCs which this case qualifies for. The histology is not supportive of an OKC.

Odontogenic keratocyst is an aggressive cyst known for its rapid growth and its tendency to invade the adjacent tissues, including bone. It has a high recurrence rate and is associated with bifid rib basal cell nevus syndrome. The majority of patients are in the age ranges of 20-29 and 40-59, but cases in patients ranging in age from 5 to 80 years have been reported. The distribution between sexes varies from equal distribution to a male-to-female ratio of 1.6:1, except in children. Odontogenic keratocyst predominantly affects Caucasian populations and, if one may judge from the limited evidence provided by the literature, is chiefly of Northern European descent.

Odontogenic keratocysts may occur in any part of the upper and lower jaw, with the majority (almost 70%) occurring in the mandible. They occur most commonly in the angle of the mandible and ramus. Posterior mandible is an area common to many benign odontogenic tumors such as ameloblastoma and odontogenic myxoma and is also a typical location for dentigerous cysts. Radiographically, OKCs present predominantly as unilocular radiolucencies with well-defined, sclerotic or scalloped borders. They may also present as multilocular radiolucencies. Odontogenic keratocysts of the maxilla are smaller in size when compared to those occurring in the mandible; larger OKCs tend to expand bone, but mildly–obvious clinical expansion (which is the case in this patient) should be viewed with suspicion for a neoplasm. OKCs can also present as small and oval radiolucencies between teeth simulating a lateral periodontal cyst, in an area of an extracted tooth simulating a residual cyst, at the apex of a vital tooth mistaken for a periapical cyst, or in the anterior maxilla between the central incisors simulating an incisive canal cyst. OKCs grow to sizes larger than any other odontogenic cysts. They usually penetrate the bone rather than expand it and grow in an anterior to posterior direction. Despite this aggressive growth, they often remain asymptomatic, thus growing to large sizes and hollowing the bone.

Odontogenic keratocysts are significant clinical entities due to their tendency for recurrence and destructive behavior. They are known to have a high recurrence rate, ranging from 13% to 60%. Complete surgical removal is the treatment of choice. Surgery includes enucleation, curettage, enucleation and peripheral ostectomy, and resection depending on the radiographic presentation, location and clinical behavior. Surgery combined with Carnoy’s solution or liquid nitrogen treatment has been effective in reducing recurrence rate. At times, adjacent or associated teeth are extracted in the interest of complete removal. Some investigators advocate marsupialization and occasionally resection of the more aggressive cysts that tend to perforate buccal and lingual bone. Resection is a rare modality of treatment. Most cysts recur within the first three years while others may recur as late as after 16 years. Conservative surgical removal and long-term follow-up is the treatment of choice by most clinicians.

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The location, age of the patient when combined with the radiographic changes of a well-demarcated unilocular radiolucency with scalloped border should make one think traumatic bone cavity (TBC) as a potential diagnosis. However, the expansion and thinning of the inferior border of the mandible, although rarely reported, is highly unusual for TBC. The histology is not supportive of this diagnosis either.

The traumatic bone cyst is best called a traumatic bone cavity since this condition does not represent a true cyst. Traumatic bone cavity (TBC) is not unique to the jawbones; it is also described in the long bones and is known as a simple solitary bone cyst occurring mostly in the humerus or femur, close to the epiphyseal plate. The long bone simple cyst is similar to the jaw traumatic bone cavity radiographically and occurs in the same age range. Trauma has been suggested as the etiology along with other non-substantiated theories such as cystic degeneration of a preexisting tumor or of the fatty marrow in the area.

Some reports suggest that it is more common in males while others report equal distribution between males and females. The long bone counterpart is more common in males by a ratio of 2.5:1. Most reports agree that the average age of occurrence is below 20 years of age. These lesions can occur, but are uncommon, over the age of 30. Kaugars reported a higher number of TBC cases in African-American females compared to the literature. The latter patients were over the age of 30. This may suggest an association with florid cemento-osseous dysplasia. The mandible is the most commonly affected area, where over 95% of cases occur, especially in the posterior premolar-molar area. TBCs are also known to cross the midline anteriorly. In one study, 27% of cases were anterior to the canine and some crossed the midline. They are usually unilocular and radiolucent, typically above the alveolar canal, and in many cases have a scalloped superior border squeezing between the roots of teeth. The latter are vital and are frequently found hanging within the empty cavity. About 25% of the lesions occur in the anterior mandible apical to the canine tooth and are usually round and unilocular; they can therefore be mistaken for periapical lesions, leading to an unnecessary endondontic treatment. Therefore, it is important to test the vitality of the teeth and carefully examine the radiographs for changes consistent with a periapical granuloma or cyst. Though expansion is not characteristic of TBC, it is described in about 26% of cases. TBCs are otherwise asymptomatic. The margins of these lesions range from very well defined to corticated to punched-out radiolucency. Pathologic fractures associated with traumatic bone cavity have been described in the jaws, but are rare. They are, however, more common in association with TBCs of the long bones.

Clinically, surgeons report an empty cavity at entrance in about two thirds of cases and cavities filled with straw-colored fluid in about one third of cases. Blood clots are also present occasionally. The bone cavity is scraped to generate bleeding, which is considered the treatment of choice for this condition. Other methods of treatment have been tried, such as packing the curetted cavity with autogenous blood, autogenous bone and hydroxyapetite. Various other reports demonstrate healing of TBC after injection of autogenous blood, after aspiration and after endodontic treatment. These lesions may spontaneously heal, but rarely. Biopsy material consists of fragments of viable bone and loose connective tissue. Osteoclast-like giant cells have also been described in a few cases. Exploration surgery usually leads to healing. Recurrence is rare.

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The unilocular radiolucency with scalloped border combined with the jaw expansion, location and age of this patient are all a good clinical and radiographic presentation for (uni)cytic ameloblastoma.

Cystic ameloblastomas constitute 13% of all ameloblastomas. They are radiographically unilocular and in 90% of the time are associated with the crown of an impacted tooth. The other 10% are unilocular radiolucency usually associated with teeth such as between teeth. The cystic ameloblastoma patients are much younger in age and are around 14-20 years of age.

Ameloblastoma, if not treated, can reach very large sizes, causing facial disfigurement. It loosens, displaces and resorbs adjacent teeth. Ameloblastomas are usually not painful unless infected, in which case they can be mildly painful. Parasthesia and anesthesia are extremely rare, unless the lesion is very large in size. Also, cystic ameloblastoma tends to expand rather than perforate the cortical bone; if the latter occurs with extension into the adjacent soft tissue, it has a higher tendency for recurrence and therefore a worse prognosis than cases in which the ameloblastoma is completely encased by bone. Curettage is the treatment of choice for the unicystic type.

References

1. Shear M. Odontogenic keratocysts: natural history and immunohistochemistry. Oral Maxillofacial Surg Clin N Am. 2003; 15: 347-362.
2. Oda D, Rivera V et al. Odontogenic keratocyst: the northwestern USA experience. J Contemp Dent Pract. 2000 Feb 15; 1(2): 60-74.
3. Zachariades N, Papanicolaou S et al. Odontogenic keratocysts: Review of the literature and report of sixteen cases. J Oral Maxillofac Surg. 1985; 43: 177-182.
4. Reichart PA, Philipsen HP. et al. Ameloblastoma: biological profile of 3677 cases. Eur J Cancer B Oral Oncol 1995;31B:86–99.
5. Julio César Bisinelli, Sérgio Ioshii, Luciana Borges Retamoso, Simone Tetü Moysés, Samuel Jorge Moysés and Orlando Motohiro Tanaka. Conservative treatment of unicystic ameloblastoma. American Journal of Orthodontics and Dentofacial Orthopedics. Volume 137, Issue 3, March 2010, Pages 396-400.
6. Gardner DG. Some current concepts on the pathology of ameloblastomas. J Oral Maxillofac Surg 1996; 82:660-669.
7. Sharma R, Marwah N. Odontogenic myxoma of the mandible: a case report. Indian J Pathol Microbiol. 2003;46:84-86.
8. Simon EN, Merkx MA. Odontogenic myxoma: a clinicopathological study of 33 cases. Int J Oral Maxillofac Surg. 2004;33:333-337.
9. Moshiri, S., Oda, D.et al. Odontogenic myxoma: a clinical and immunohistochemical study. J Oral Path 1992;21:401-403.
10. Kumar ND, Sherubin JE, Raman U, Shettar S. Solitary bone cyst. Indian J Dent Res. 2011 Jan-Feb;22(1):172-4.
11. Kahler B. Traumatic bone cyst suggestive of a chronic periapical abscess: A case report. Aust Endod J. 2011 Aug;37(2):73-5.

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The size, location, gender and jaw expansion are all in support of the behavior of a neoplasm including that of an odontogenic origin such as that of odontogenic myxoma. The radiographic finding of a unilocular radiolucency with scalloped border is rarely described in odontogenic myxoma but can be supportive. Odontogenic myxomas tend to be multilocular. The age of this patient is on the younger age range of this condition but that will not deter the condition to be considered on the differential diagnosis. The histology however, is not supportive of an odontogenic myxoma.

Odontogenic myxoma occurs in the jaw bones, usually in the tooth-bearing areas of the jaw. It is an uncommon, benign, but locally aggressive neoplasm. Nearly all cases so far have been described in the jaw bones. Therefore, it is of tooth origin, and is believed to be from the mesenchymal portion of a tooth germ, most likely of the dental papilla. It has the potential for extensive bony destruction and extension into the surrounding structures. It is less common than odontomas and ameloblastomas. For that reason, a pathologist who is not familiar with the histology of a tooth germ can mistake a myxoid dental follicle for an odontogenic myxoma. Almost 75% of odontogenic myxomas occur in patients around 23-30 years of age with a slight female predilection (1:1.5 male-to-female). It rarely occurs in patients over 50 or under 10 years of age. It occurs almost equally in the maxilla and mandible with a slight predilection for the posterior mandible. A few cases are described in the ramus and condyle, non-tooth bearing areas.

Odontogenic myxoma is slow-growing, persistent and destructive. Most cases are expansile and can displace and resorb teeth. In the maxilla, they usually invade the maxillary sinuses and at times (though rarely) cross the midline to the opposing sinus. Radiographically, the majority present as expansile and multilocular, though some are unilocular with or without scalloped borders, and rare cases present with a diffuse and mottled appearance which can be mistaken for a malignant neoplasm. Grossly, this lesion is gelatinous in nature, making curettage alone difficult; the more fibrotic odontogenic myxomas (also known as odontogenic myxofibroma or fibromyxoma) have more body and are easier to curette. Histologically, it is made up of loose and delicate fibrous connective tissue. The fibroblasts are stellate and are suspended on a delicate network of collagen fibrils. Immunohistochemistry studies suggest that the spindle-shaped cells constituting this neoplasm have a combined fibroblastic and smooth muscle typing, suggesting that it is of myofibroblastic origin. Small blood vessels are present, as are small odontogenic epithelial islands on occasion. Sometimes, this lesion is fibrotic, making it easier to curette.

The treatment of choice is surgical excision ranging from segmental resection with clear bony margins of up 1.5cm to prevent recurrence of the neoplasm. Curettage is with and without cauterization is used for treatment, but is associated with a high recurrence rate. Reconstruction can be immediate or delayed, and can include an autologous bone graft from the anterior or posterior iliac crest. Fibula-free vascular osteocutaneous bone graft is another reconstructive modality, as is distraction osteogenesis. Immediate postoperative follow up is weekly for approximately one month, then monthly for the next five months and twice a year for the next five years.