Radicular cysts are the inflammatory odontogenic cysts associated with a non-vital tooth. A residual radicular cyst, which is often referred as residual cyst, is also a radicular cyst that remains following the extraction of the associated tooth. Periapical cyst and apical periodontal cyst are also synonyms of the radicular cyst [1–3].

Radicular cysts represent 55% of all odontogenic cysts which makes them the most common cyst of the jawbones. They mostly occur due to dental caries which cause pulpal necrosis [1].

They are mostly located at the apex of the teeth but radicular cysts that occur at the apex of lateral root canals are also reported and they are known as “lateral radicular cysts” [2].

The most important differential diagnosis tool for radicular cysts is they are always associated at the apex or lateral of a non-vital tooth; thus, vitality test plays a crucial role [2, 3].

Unless they cause expansions they are detected incidentally on routine radiographs as round or oval, well-defined, unilocular radiolucent lesions at the apex of a non-vital tooth. Residual radicular cysts have the same radiographical features with radicular cyst; however, they are located at previously extracted teeth sites. Eventhough they are inflammatory odontogenic cysts, they can get secondarily infected and cause destructions at buccal and lingual cortical plates [1–3]. (Figs. 17.1 and 17.2). See also Chap. 16 for more detailed information on periapical diseases.

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig1_HTML.jpg — Fig. 17.1

A: Radicular Cyst/B: Residual Cyst. A: OPG reveals unilocular radiolucent lesion with a cortical well-defined border at maxillary anterior site. Roots of three teeth with crowns are seen in relation to the lesion. B: Unlike Fig. 17.2A, a unilocular radiolucent lesion with a corticated well-defined border is seen in the edentulous mandibular left posterior site

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig2_HTML.jpg — Fig. 17.2

A: Secondarily Infected Radicular Cyst/B: Residual Cyst. A: Axial CBCT slice reveals the destruction of the buccal and palatal cortical plates of the maxilla. Although odontogenic cysts cause expansion instead of destruction, secondarily infected cystic lesion cause more aggressive lytic patterns. B: Axial CBCT slice reveals unilocular hypodense lesion with hyperdense corticated well-defined border at edentulous site

Common sonographic features of radicular cysts are (Fig. 17.3):

Lesions without bone perforation or destruction at cortical plate or any bone dehiscences may not have ultrasonography findings due to artifacts such as acoustic shadowing.
Internal Structure: Homogeneous anechoic internal structure is generally seen without any hyperechoic focis.
Peripheral Structure: Well-defined hyperechoic oval or round borders are generally seen.

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig3_HTML.jpg — Fig. 17.3

Radicular Cyst. US reveals unilocular homogeneous anechoic lesion with a well-defined hyperechoic oval border. Acoustic enhancement is not clearly visible although the appearance suggests a cystic lesion

17.1.2 Inflammatory Collateral Cysts

Inflammatory collateral cysts are two entities which were known as buccal bifurcation cysts and paradental cysts. They account for 5% of odontogenic cysts. Most of the paradental cysts are associated with mandibular third molars and most of the buccal bifurcation cysts are associated with mandibular first molars [1].

Paradental cysts are well-defined, unilocular, radiolucent lesions which have similar features with dentigerous cyst. Paradental cysts are associated with partial unerupted teeth while dentigerous cysts are associated with complete unerupted teeth. Paradental cysts and pericoronitis share some clinical and radiographic features and WHO stated that “Paradental cysts are usually associated with a history of longstanding pericoronitis.” [1].

Buccal bifurcation cysts are also well-defined, unilocular, radiolucent lesions and they have a characteristic clinical feature called “tilting.” The crowns of the affected teeth are tilted buccally due to the lesion. They are generally painless swellings [1–3].

17.2 Developmental Odontogenic Cysts

17.2.1 Dentigerous Cyst

Dentigerous cyst is an odontogenic cyst that is attached to the cervical region of an unerupted tooth and envelops the crown. Eruption cyst is a variant of dentigerous cyst found in the soft tissues overlying an erupting tooth [1].

Dentigerous cysts are developmental odontogenic cysts which are attached to the cementoenamel junction of an unerupted tooth. “Follicular cyst” is the synonym of the dentigerous cysts [2–4]. They cover the crown portion of the tooth. Dentigerous cysts which are located in the soft tissues are known as eruption cysts and they are not frequent since they only account for less than 2% of the cases [1].

Dentigerous cysts are the second most common cyst in the jaws and they represent 20% of the odontogenic cysts [1]. The most common teeth which are associated with dentigerous cysts are the mandibular third molars. Mandibular third molars represent 75% of the dentigerous cysts. Maxillary canines and maxillary third molars are the most frequent associated teeth after mandibular third molars [1–3] (Fig. 17.4).

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig4_HTML.jpg — Fig. 17.4

Dentigerous Cysts of three different cases. A: OPG reveals a unilocular radiolucent lesion with well-defined borders attached to the molar tooth’s crown. The lesion extends from the left coronoid process of the mandible to the mandibular left molar site. B: OPG reveals a unilocular radiolucent lesion with well-defined borders attached to the cementoenamel junction of a vertical impacted molar tooth. C: OPG reveals a unilocular radiolucent lesion with well-defined borders which seem like surrounding the whole teeth. Circumferential type dentigerous cysts appear as they contain within although they are also attached to the cementoenamel junction of a tooth. CBCT is useful while evaluating lesions with relevant radiographic features

As the other developmental cysts, small lesions are generally asymptomatic; however, they can reach great sizes and cause expansions at cortical bones (Fig. 17.5). Secondarily infected dentigerous cysts may cause pain and swellings [2].

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig5_HTML.jpg — Fig. 17.5

Dentigerous Cyst. Coronal CBCT slice of the of Fig. 17.5A. Lesion’s attachment to the cementoenamel junction and the expansions of the buccal and lingual cortical plates are seen

Radiographically, OPG reveals a corticated well-defined periphery structure and a unilocular radiolucent internal structure that is attached to the cementoenamel junction of an unerupted tooth. The lesion envelops the crown portion of the tooth. CBCT reveals expansion at buccal and lingual cortical borders and inferior displacement of the mandibular canal/superior displacement of maxillary sinus floor for larger lesions [2–4].

Common sonographic features of dentigerous cysts are (Fig. 17.6):

Lesions without bone perforation or destruction at the cortical plate or any bone dehiscences may not have ultrasonography findings due to artifacts such as acoustic shadowing.
Internal Structure: Heterogeneous hyperechoic and hypoechoic areas one within each other which creates an appearance of “snow-flakes internal structures” which is common for dentigerous cysts.
Peripheral Structure: Well-defined/moderately-defined borders can be seen. Since dentigerous cysts are intraosseous lesions deep portions of the lesion are not detectable with US.

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig6_HTML.jpg — Fig. 17.6

Dentigerous Cyst. US reveals unilocular heterogeneous mixed internal structure with “snow-flake” radiographic appearance. Deep portions of the lesion are not clearly seen with US since the lesion is an intraosseous lesion which did not cause thinning or perforation at the cortical plate

17.2.2 Odontogenic Keratocyst

With the novel 2017 WHO classification, odontogenic keratocyst (OKC) was reclassified as an odontogenic cyst [1, 5, 6]. OKC is an odontogenic cyst characterized by a thin, regular lining of parakeratinized stratified squamous epithelium with palisading hyperchromatic basal cells. OKCs represent 10–20% of odontogenic cysts and following the radicular cyst and dentigerous cyst they are the most common odontogenic cyst. 5% of all OKCs are associated with Gorlin-Goltz Syndrome (Nevoid Basal Cell Carcinoma) and multiple OKCs are seen with this syndrome [1].

Mandibular posterior site and mandibular ramus are the most common localization for the OKCs as the lesion at these localization accounts for 80% of all OKC cases [1, 7]. Instead of causing expansion at buccal and lingual cortical plates, OKCs grow in anterior-posterior direction. Since they do not cause expansion or cause only minimal expansion they are mostly seen in routine radiographic examinations. Small lesions can be completely asymptomatic; however, large lesions can even displace the orbits [1–4, 7].

Radiographically, OPG reveals corticated well-defined radiolucent lesions. They can be multilocular or unilocular. Additional to OPG images, CBCT reveals the minimal-expansive or non-expansive nature of the lesions (Figs. 17.7 and 17.8) [1–4, 7]. Since those lesions do not tend to expand or destroy the cortical plates US imaging of OKCs are limited. If OKCs get secondarily infected they can also cause destructions at cortical plates.

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig7_HTML.jpg — Fig. 17.7

Odontogenic Keratocyst. OPG reveals a unilocular radiolucent lesion with well-defined borders which extends from the right coronoid process of the mandible to the mandibular right molar site. Note the mandibular canal which is dislocated inferiorly due to the lesion (red arrow). Due to the extraction of the mandibular right third molar, a more radiolucent area is seen at the post-molar site (turquoise arrow)

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig8_HTML.jpg — Fig. 17.8

Odontogenic Keratocyst: Axial CBCT slice of Fig. 17.8 reveals a minimal expansive lesion despite extending from coronoid process to molar region which is one of the key radiographic features of odontogenic keratocyst

Common sonographic features of odontogenic keratocysts are (Fig. 17.9):

Lesions without bone perforation or destruction at cortical plate or any bone dehiscences may not have ultrasonography findings due to artifacts such as acoustic shadowing.
Internal Structure: Homogeneous anechoic internal structure is generally seen without any hyperechoic focis. If foci present, the appearance turns to be heterogeneous hyperechoic and hypoechoic areas one within each other which creates an appearance of “snow-flakes internal structures.”
Peripheral Structure: Well-defined hyperechoic oval or round borders are seen.

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig9_HTML.jpg — Fig. 17.9

Odontogenic Keratocyst. US reveals a unilocular anechoic internal structure (A) and a unilocular heterogeneous mixed internal structure of two cases. While acoustic enhancement is seen in Fig. 17.7B it is not visible in Fig. 17.7A. Since odontogenic keratocysts do not cause perforations or destructions at cortical plates it is possible that US examination might not demonstrate the internal structure of the lesion clearly

17.2.3 Lateral Periodontal Cyst and Botryoid Odontogenic Cyst

Lateral Periodontal Cyst and Botryoid Odontogenic Cyst are developmental odontogenic cysts which are located at the lateral of the erupted teeth’s roots. They are both detected as incidental findings on routine radiographs due to their asymptomatic nature. While lateral periodontal cyst is a unilocular cyst, botryoid odontogenic cyst is a multilocular cyst. Both of these cysts usually have a cortical well-defined periphery structure and radiolucent internal structures on OPGs [1–4] (Fig. 17.10).

../images/484215_1_En_17_Chapter/484215_1_En_17_Fig10_HTML.jpg

Tags: Ultrasonography in Dentomaxillofacial Diagnostics

Aug 7, 2022 | Posted by mrzezo in Oral and Maxillofacial Radiology | Comments Off

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of Ultrasonography in Maxillofacial/Intraoral Inflammatory and Cystic Lesions

17. Applications of Ultrasonography in Maxillofacial/Intraoral Inflammatory and Cystic Lesions