What Are Residual Cysts of the Jaw?
Residual cysts may be defined in oral pathology as retained radicular cysts without the presence of an offending tooth or dentition. Cysts of the jaws, based on their origin, are mainly classified into odontogenic or non-odontogenic cysts. Cysts of odontogenic origin are the most prevalent type of oro-dental cysts which develop from the epithelium of the developing dentition present in individuals of all age groups.
Residual cysts may account for up to eight percent of all presenting jaw cysts and are seen in populations between the second and eighth decade of life with the highest prevalence in the middle-aged population from the third decade of life.
What Is the Cause of Residual Cysts?
The origin of the epithelial covering of these residual cysts may be attributed to the developing dental organ, cell rests of Malassez, reduced dental epithelium, or fragments of the dental lamina. These epithelial remnants may lead to cystic development or transformation when the associated tooth is extracted. Hence, the residual cysts can be attributed as a post-extraction complication of the traumatized tooth. Owing to etiopathogenesis, residual cysts may be regarded as rare inflammatory jaw cysts.
In the absence of any associated tooth or offending dentition, these cysts have been identified as radicular cysts in some histopathologic studies. Pertaining to its potential mimic nature, the cyst shows great similarity to aggressive cysts or tumors of the jaws that need to be differentiated accurately by the dental surgeon through panoramic imaging or, ideally, CBCT (cone beam computer tomography) studies. Diagnostic imaging should be followed with histopathologic examinations to correlate the radiographic with the microscopic findings.
What Is the Pathogenesis of Residual Cyst?
The pathogenesis is mainly initiated via bacterial spread originating from a non-vital tooth and eventually into the periapical region of the jaw. Left untreated, the chronic jaw infection may subsequently manifest into a periapical granuloma within the edentulous region comprising activated T-cells, cytokines, etc. The cytokines or inflammatory pro-mediators then act upon the epithelial remnants to proliferate and differentiate into cysts. The proliferating epithelium also turns oedematous by an accumulation of fluid and may further coalesce to form micro cysts. If micro cysts are observed in these lesions, they are lined by epithelial cells composed of inflammatory infiltrate. Cholesterol clefts or cyst calcifications are rare but noticeable. The cystic wall is a semi-permeable membrane through which the cyst expands by osmotic diffusion. The complications associated with an expanding residual cyst lesion are due to the lytic by-products released from the epithelial or inflammatory cells which increases the osmotic pressure and can produce large intra-osseous cystic lesions within the jaws.
What Is the Potential, Spread, and Diagnostic Challenge Faced With Residual Cysts?
Residual cysts rarely transform into squamous cell carcinomas, but limited evidence and case reports have shown the potential of chronic untreated residual cysts triggering or transforming into a squamous cell carcinomatous lesion owing to the cyst’s aggressive and asymptomatic bone invasion capability and cervical lymph node involvement. Residual cysts may present like any other dental cyst with similar features to that of conventional radicular cysts.
Due to the etiopathogenesis of the cyst, the causative agent gets removed through extraction, so the inflammatory infiltrate within the cystic space is a remnant of the cause. The size of the cyst also decreases with the development of non-inflammatory and fibrous collagen tissues coated along the cystic walls. These cysts pose a diagnostic challenge, even by histologic examination, because of the thin epithelial lining. Traditionally, studies have shown an active growth pattern in these cysts, especially in non-rehabilitated edentulous regions where there is significant bone resorption.
How Do Residual Cyst Present on Radiographs?
The radiographic presentation of these cysts gives a unilocular, well-defined, radiolucent appearance in 2-D imaging like IOPA (intra-oral periapical radiograph) and OPG (orthopantomogram). They may be rounded or oval-shaped with thin sclerotic borders.
What Is the Differential Diagnosis of Residual Cysts?
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Traumatic bone cyst.
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Odontogenic keratocyst.
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Unicystic ameloblastoma.
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Glandular odontogenic blastocyst.
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Ciliated surgical cyst.
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Radicular cyst.
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Periodontal cyst.
How to Manage Residual Cysts?
Depending upon the extent, recurrence rates, and history of previous lesions, residual cysts can be treated by the dental or the maxillofacial surgeon by:
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Enucleation: It is a surgical technique, wherein the entire content of the residual cyst will be extracted. It is routinely preferred for smaller lesions, alongside biopsy can be done with the part of the lesion to analyze and evaluate the cellular nature of the cystic content.
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Marsupialization: Enucleation cannot be employed for extensive residual cyst due to larger area of involvement. In such cases, marsupialization technique is advised, which helps to collapse the dimension of the cyst to an extend that it can be finally enucleated.
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Decompression: It is the most conservative strategy to deal with residual cyst, which work by gearing down the intraluminal pressure within the cyst. The gathered fluid within the cyst is made of seep out by creating tiny window like opening in the cystic walls, which facilitates the down regulation of the intra-cystic pressure.
The enucleation method is considered a more acceptable method for treating residual cysts in order to prevent the recurrence of the cyst and also has low morbidity.
What Is the Prognosis of Residual Cysts?
Follow-ups have revealed that the cysts do not recur after appropriate excision but may leave behind intraosseous fibrous scars. The lack of recurrence portrays a good prognosis after surgical excision.
Conclusion
Residual cysts are asymptomatic and potentially mimic aggressive cystic lesions that may have a malignant transformation potential to squamous cell carcinomas and require further research. These cystic lesions hence need to be managed by the dental surgeon. Enucleation not only eliminates the cyst completely but also provided a long-term prognostic value and prevents any possible recurrence.
