Recently, I encountered two situations that inspired this article. I came across a periapical radiograph of a new patient who had a radiolucency, which presented as a well-defined lesion distal to an extracted mandibular second molar. The extraction was done about six months ago.
Another incident was when a new patient with a unilocular lesion at the apex of #29 was referred to an endodontist. The endodontist performed root canal treatment. However, the lesion was still present radiographically months after the treatment without changes in its appearance and size.
Cyst vs. Abscess
Differentiating between a cyst and an abscess can sometimes be challenging. Knowing the common cysts, their etiology, and specific features minimize misdiagnosis.
A cyst is a sac that is lined with epithelium tissue and is enclosed by connective tissue, which can be filled with, for example, fluid, hair, or blood.1 The types of cysts are determined by their origin and location.
An abscess usually happens as a result of:
- Gross decay that is left untreated
- Secondary to any dental decay
- Trauma to a tooth
- Poor oral hygiene
- Initial root canal therapy2,3
The severity of the abscess depends on the level of virulence of the bacteria (mostly anaerobes), the individual’s oral hygiene, and immune response.2,3 These bacteria can reach the tooth via any opening, such as failed restorations, trauma to the soft and hard tissue of the tooth, and fractures.2 The bacteria can cause infection within the tooth, can move towards the tooth canal and then accumulate at the apices of the tooth.2,3
Accumulation of bacteria leads to infection, which may cause pain, fistula, bad taste in the mouth, and severe problems such as “septicemia, cavernous sinus thrombosis, brain abscess, shock, and occasionally death” if left untreated3 (see Image 1).
Mistaken for an Abscess
Sometimes it is hard to differentiate a cyst from an abscess. Knowing the common location of certain cysts and their appearance may help to minimize misdiagnosing. Some cysts that are potentially problematic when making a definitive diagnosis are nasopalatine duct cyst, central giant cell granuloma, periapical cyst, lateral periodontal cyst, dentigerous cyst, and odontogenic keratocyst, as they can resemble an abscess.1,2,5-7
Nasopalatine duct cyst: This occurs around the nasopalatine canal, and it has a heart shape and a well-defined appearance.1 Pain may or may not be present, and treatment includes cyst removal.1 Radiographically, a heart shape (or sometimes a tear shape), unilocular radiolucency is present at the apex of 8 and 9.1 (see Images 2 and 3)
Central giant cell granuloma: It appears as a multilocular lesion on a radiograph and is bigger than an abscess in size and shape; therefore, it should not be mistaken for an abscess1 (see Image 4).
Periapical cyst: Also known as a radicular cyst, this is the most common oral cyst that occurs around the apices of a nonvital tooth and mostly around anterior maxillary teeth.1,2 It is mostly asymptomatic, and radiographically a unilocular, well-defined radiolucency at the apex of the tooth is present.1 If the cyst is not treated properly, it can lead to a residual cyst.1,5 The treatment consists of tooth and cyst removal. However, if it is mistaken for a dental abscess, the cyst stays in the area after the root canal treatment.1 To see radiographic images of a radicular cyst, click here.
Lateral periodontal cyst: This cyst is unilocular, radiolucent, well-defined, and lateral to the tooth, which usually occurs around mandibular premolars and canines, even though it can be found around maxillary premolars and canines as well.1 This cyst is asymptomatic and occurs in vital teeth, so the patient may not be aware of its presence.1 The treatment is excisional with an excellent prognosis1 (see Image 5).
Dentigerous cyst: The asymptomatic and the second most common cyst happens around the crown of an impacted tooth, unerupted tooth, supernumerary tooth, or odontoma.1 Therefore, it is not unexpected to see this cyst around the impacted third molars of young adults. This cyst appears well circumscribed on a radiograph.1 To treat this cyst, tooth extraction and excisional removal of the cyst proved to have an excellent prognosis, although the area must be evaluated regularly for ameloblastoma1 (see Image 6).
Odontogenic keratocyst (OKC): Being a very destructive cyst, it accounts for 10% of all odontogenic cysts, with three times the occurrence rate in the mandible than in the maxilla and some cases invading the ramus.1,6,7 The individual may or may not have any pain; however, the cyst may cause external root resorption.1 This cyst can be either unilocular or multilocular.4 If unilocular, it may be mistaken for another cyst or a dental abscess if the tooth is nonvital.4 Since this cyst has a high recurrent rate (about 60%), it must be monitored frequently by taking proper radiographs and CT scans during the recall appointments1 (see Image 7).
The following table helps with differentiating these common cysts that can be mistaken for an abscess.
|Cyst||Radiographic Appearance||Common Location||Pain or No Pain||Unique Specification|
|Nasopalatine duct cyst||Heart-shape unilocular||Nasopalatine canal. Around teeth #8 and 9||May or may not be present||Heart-shaped|
|Periapical cyst, aka radicular cyst||Unilocular radiolucency at the apex||Maxillary anterior, although can happen around all the apices of all the teeth||Asymptomatic||The most common cyst, occurs around nonvital teeth|
|Lateral periodontal cyst
|Unilocular, well-defined, lateral to the tooth||Favors mandibular premolars and canines||Asymptomatic||Occurs around vital teeth|
|Dentigerous cyst||Well circumscribed||Associated with impacted teeth, unerupted teeth, supernumerary teeth, or odontoma||Asymptomatic||The 2nd most common cyst|
|Odontogenic keratocyst (OKC)||Unilocular or multilocular||Three times higher in mandibular teeth than maxillary teeth||Pain may or may not be present||The 3rd most common cyst, external root resorption may be present|
To conclude, a cyst may resemble an abscess. The treatment of each lesion is different. Patients usually do not experience pain with a cyst, unlike an abscess.1 Moreover, treatment of an abscess may be based on the prognosis, location, and type of the abscess. Therefore, knowing the most common cysts may help to close this gap If in doubt, it is better to refer patients to an endodontist or an oral surgeon for further evaluation.
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- DeLong, L., Burkhart, N.W. (2012). Radiolucent Lesions. In General and Oral Pathology for the Dental Hygienist (2nd ed., pp. 517-548). Jones and Bartlett Learning.
- Sanders, J.L., Houck, R.C. Dental Abscess. [Updated 2022 Feb 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK493149/
- Shweta, S., Prakash, K. Dental abscess: A microbiological review. Dental Research Journal. 2022; 10(5): 585-591. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3858730/
- Dave, M., Clark, L., Grindrod, M., et al. Adapting treatment approaches for dentigerous cysts in pediatric and adult patients: A case series. Oral Surgery. 2019; 14(3): 277-284. https://doi.org/10.1111/ors.12575
- Gnepp, D.R. (2021). Odontogenic Cysts and Tumors. In V.I. Woo, A.C. Chi, B.W. Neville, Gnepp’s Diagnostic Surgical Pathology of the Head and Neck (3rd ed., pp. 827-880). Elsevier. https://doi.org/10.1016/B978-0-323-53114-6.00010-9
- Borghesi, A., Nardi, C., Giannitto, C., et al. Odontogenic keratocyst: imaging features of a benign lesion with an aggressive behaviour. Insights into Imaging. 2018; 9(5): 883-897. https://doi.org/10.1007/s13244-018-0644-z
- Harmon, M., Arrigan, M., Toner, M., O’Keeffe, S.A. A radiological approach to benign and malignant lesions of the mandible. Clinal Radiology. 2015; 70(4): 335-350. https://doi.org/10.1016/j.crad.2014.10.011