Apical Granuloma: Etiology, Anatomic Pathology, Clinical Manifestations, and Treatment

Apical granuloma, or periapical granuloma, is the most common form of chronic apical periodontitis (AP). It is an inflammatory lesion composed of granulomatous tissue rich in lymphocytes, macrophages, and plasma cells.

Chronic AP is a long-term inflammatory process affecting the tissues around the root apex of the tooth. This condition leads to periapical bone resorption, which has no significant clinical symptoms but is detectable on radiography.

Etiology

Chronic inflammation in the periapical region is primarily triggered by a bacterial infection of the root canal system. In teeth that have not previously undergone endodontic treatment, AP serves as a protective response to the primary infection in the necrotic pulp. Another possible etiological factor is a secondary infection, introduced into the root canal system due to endodontic treatment (e.g., inadequate isolation during the procedure, improper obturation, or insufficient coronal sealing). Moreover, extrusion of chemical agents and root-filling materials beyond the apical foramen can lead to toxic tissue damage. Substances like talc, calcium salts, cellulose from paper points, or cotton fibers may promote the formation of a foreign body giant cell granuloma. Additionally, a foreign material in the periapical region may become a perfect substrate for a biofilm.

Types of microorganisms detected in teeth with AP:

• Primary infections: Dialister, Bacteroides, Pseudoramibacter, Porphyromonas, Treponema, Filifactor, Tannerella, Prevotella, Enterococcus, Veilonella, Olsenella, Pyramidobacter, Campylobacter, Propionibacterium, Streptococcus, Parvimonas, Fusobacterium, Eikenella, Actinomyces.
• Previously treated teeth: Enterococcus faecalis (the most commonly identified species), Pseudoramibacter alactolyticus, Propionibacterium, Filifactor alocis, Dialister pneumosintes, Tannerella forsythia, Parvimonas micra, Prevotella intermedia, Treponema denticola, Candida albicans.

The necrotic pulp within the root canal system provides an ideal environment for bacterial colonization and functioning. Here, bacterial aggregates are enclosed in an extracellular matrix and organized into biofilms that attach to the walls of the root canals. In this form, microorganisms are protected from the host immune system, as defense mechanisms cannot function effectively within the poorly vascularized root canal. Furthermore, the biofilm structure makes bacteria more resistant to a variety of antibacterial agents. If the biofilm in the root canal is not eradicated or substantially disrupted, AP may become chronic as the pathogens will persist. Histologically, macrophages and lymphocytes are the primary and predominant cells in this process, with occasional foam and giant cells observed.

The hallmarks of chronic AP are bone resorption in the periapical region and proliferation of fibrovacular granulation tissue. The former process is triggered by activated osteoclasts, while the latter represents an attempt to repair tissues and limit the inflammatory process. It is worth mentioning that resorption may also affect apical fragments of the tooth root.

Outcomes

The possible outcomes of apical granuloma include:
– Healing of the periapical tissues following successful endodontic treatment;
– Progression to an acute or chronic apical abscess if the source of infection persists and the host immune response is compromised by exposure to bacterial infection.

Anatomic Pathology

Depending on the etiology, the following anatomical changes may be observed in the affected tooth:

• a deep carious lesion penetrating into the dental pulp;
• signs of compromised sealing in a restoration adjacent to the pulp tissues (e.g., defects, cracks, marginal pigmentation, or secondary caries);
• signs of trauma, such as cracks, dentin chipping, or pulp exposure.

This condition is characterized by necrotic pulp that appears yellowish-gray or grayish-black. At the root apex, there is a focus of destruction of the periodontal ligament and bone, filled with granulomatous tissue.

This tissue is infiltrated by mast cells, macrophages, lymphocytes, plasma cells, and occasionally polymorphonuclear leukocytes. In addition, multinucleated foreign body giant cells, foam cells, cholesterol crystals, and epithelial cells in the form of disorganized strands can be present. In the peripheral area, fibrous tissue is usually observed.

Diagnosis

• Medical history.
• Clinical examination: visual examination, percussion of the tooth, palpation along the mucobuccal fold, periodontal probing, and assessment of tooth mobility.
• Pulp sensibility tests (thermal and electrical).
• Radiography (intraoral contact radiography, radiovisiography, orthopantomography, or cone-beam computed tomography): a carious lesion, restoration, or traumatic defect penetrating into the pulp chamber may be revealed. A periapical radiolucency, indicating bone destruction, may appear as a round or irregularly shaped radiolucency with well-defined borders around the root apex. A two-dimensional (2D) X-ray might only show a widened periodontal ligament space with no clear periapical radiolucency if the cortical plate remains intact.
• Currently, there are no noninvasive diagnostic methods capable of distinguishing a granuloma from a cyst. A definitive diagnosis can only be made based on biopsy results.

Clinical Manifestations

The condition is usually asymptomatic. On visual examination, a tooth with a deep carious lesion, restoration, or traumatic defect penetrating the pulp chamber is observed.

Percussion of the tooth is typically painless, as is the palpation of the mucobuccal fold. However, if the cortical plate is involved, palpation may cause discomfort. There is usually no response to thermal or electrical pulp testing. Gingival probing depth remains within normal limits (1–3 mm), and the tooth mobility is physiological.

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Treatment

Although it is impossible to make a differential diagnosis with other forms of apical periodontitis on the basis of radiography, and the histologic status is usually unknown, the treatment consists of eliminating the etiologic factor. Endodontic treatment of the tooth is performed: extirpation of necrotic pulp or removal of old filling material from the root canals, mechanical and medical treatment of root canals, obturation with subsequent restoration of the tooth.

If access to the source of infection is difficult, in addition to conservative endodontic treatment, microsurgical methods (periradicular curettage, resection of the root apex with retrograde filling, amputation of the tooth root), intentional replantation are used.

In cases where endodontic treatment may have unfavorable outcomes, tooth extraction is indicated.