Teaching Case

A 61-year-old woman presented with episodes of paresthesia in the region of the left mental nerve and a slowly enlarging swelling of the left mandible for the past 2 years.

A Cone Beam Computed Tomography (CBCT) showed a large radiolucent lesion in the left mandible with cortical breakthrough of the buccal cortex with an associated soft tissue component (Fig. 1a). The mesiodistal extent was larger than the buccolingual extension. (Fig. 1a) The roots of teeth 35 and 34 are located in the cyst (Fig. 1b, 2). The intimate relationship of the lesion with the mandibular canal may explain the paresthesia in the region of the left mental nerve (Fig. 2). Magnetic resonance imaging (MRI) showed an intramedullary lesion in the left mandible with scalloping of the lingual cortex and breakthrough of the buccal cortex (Fig. 4). The lesion was isointense to muscle on T1-WI (Fig. 3) and hyperintense on T2-WI with intralesional areas of intermediate signal (Fig. 4b). After gadolinium contrast administration, there was weak peripheral rim enhancement (Fig. 5a-b). Surgical enucleation revealed a cystic lesion containing keratin. On histopathological examination, the cyst wall consists of keratinised squamous epithelium.

Based on the imaging and histopathologic findings, the diagnosis of odontogenic keratocyst (OKC) was made. OKC is a developmental odontogenic cystic lesion arising from additional remnants of the dental lamina of the jaw bones or the basal cells from the oral epithelium. OKCs represent 2-11% of all odontogenic cysts, affect all ages with a peak from the 2nd–4th decade and have a male to female ratio of 2:1 [1, 2]. Clinically, most OKCs are asymptomatic but symptoms like pain, swelling and paresthesia of the lower lip can be seen in larger lesions [2, 3)]. In children, they are often associated with basal cell naevus syndrome (NBCCS or Gorlin’s syndrome), consisting of multiple OKCs, skin basal cell carcinomas, skeletal abnormalities and falx calcifications [2]. Radiologically, OKCs are difficult to differentiate from other radiolucent odontogenic lesions. A panoramic radiograph typically reveals a radiolucent unilocular or multilocular lesion with well-demarcated or scalloped margins. Larger lesions tend to be more multilocular [2]. Most lesions (75%) are located in the posterior mandible with 50% occurring at the angle. Other lesions are located in maxilla with a possible expansion into the maxillary sinus. In 25%-40% an impacted tooth is seen and therefore it can be difficult to differentiate from a dentigerous cyst. Teeth displacement may occur but root resorption is very rare [1]. (CB)CT shows similar features as panoramic radiographs but (CB)CT is superior to determine lesion extension and cortical thinning or breakthrough [4]. OKC tend to grow in a mesiodistal direction while ameloblastomas usually show a predominant buccal-lingual expansion [2]. On MRI, the signal may vary, whereas ameloblastomas are hypointense on T1 and hyperintense on T2-WI [5-7]. There is a weak enhancement of the rim in OKCs whereas ameloblastomas display a nodular enhancement pattern [2, 8]. Diffusion-weighted imaging (DWI) can be used to differentiate between OKCs and ameloblastomas. OKCs contain desquamated keratin which increases the viscosity and therefore may cause diffusion restriction. Ameloblastomas containing proteinaceous fluid do not show restricted diffusion [6]. In case of NBCCS, (CB)CT and MRI can be used to detect multifocality. Because imaging features may be nonspecific, histological confirmation is mandatory [2]. The cyst wall is composed of a keratinised squamous epithelium. Treatment of OKCs depend on age, size and location of the cyst and soft tissue expansion. Treatment options are enucleation, marsupialisation, curettage and osteotomy [4]. Regular follow-up for 5 years is recommended as the recurrence rate is high [1].

Written informed patient consent for publication has been obtained.