Odontogenic choristoma embedded in the cheek of an old patient

Abstract

Odontogenic choristomas are a rare and recently classified entity, defined as neoplasms containing tissues of odontogenic derivation, found in abnormal locations and usually diagnosed in the early age. The authors report a unique case of a 79-year-old patient who presented to our attention for a skin lesion in the right cheek with no history of trauma or recent dental procedures, that underneath presented an indolent tooth-like structure inside the soft tissue of the right cheek, which at the histological study resulted to be an odontogenic choristoma. This rare histopathological diagnosis should be considered when a hard lesion is present in the head and neck region.

Background

Odontogenic choristomas are a rare histological entity, defined as neoplasms containing tissues of odontogenic derivation, found in abnormal locations,¹ like tongue,² cheek³ or even outside of the mouth, like near the eye.⁴ To date, less than 10 reports describe this entity in literature and most of them are diagnosed in the early stage of life.³ The authors report a unique case of an old patient who presented to our attention for a skin lesion in the right cheek with no history of trauma or recent dental procedures, that at the objective examination presented an indolent stiff formation underneath the skin surface, that radiologically was described as a tooth-shaped structure inside the soft tissue of the right cheek. At the histological study, the formation resulted to be an odontogenic choristoma.

Case presentation

A 79-year-old woman coming from a rural area of Italy presented to our attention for a skin lesion located in the right cheek. At the medical interview, the patient referred since childhood the presence of a hard, firm lesion that started itching 3 months before the visit, not following any recent trauma, intraoral infection or surgical procedure. At the objective examination, a 1.2×1 cm reddish plain lesion was present, located in the right cheek, 8 mm lateral to the right ala nasi (figure 1). Oral examination revealed complete edentulism due to the age of the patient. At the palpation, a firm, stiff, subcentrimetic formation was detectable just deep and medially to the skin lesion located in the right cheek.

Figure 1.

Case presentation at the first visit.

Investigations

Before our first visit, the patient never performed any radiological examination of the head and neck district (orthopantomography or CT scan). Hence, a maxillo-mandibular CT scan was performed to better establish the lesion origin and borders, revealing the presence of a hard radiopaque structure with a dimension of 0.9×0.5×0.3 cm that was included in the subcutaneous tissue (figure 2).

Figure 2.

Sagittal CT scan highlighting the presence of a radiopaque formation, lateral to the nose.

Treatment

Two weeks later, the patient gave a written informed consent for the excision and histopathological analysis of the neoplasm; locoregional anaesthesia on the right cheek of the patient was performed, followed by surgical excision of the cutaneous lesion with a 0.5 cm margin, as well as the removal of the hard tissue formation that was reported on the CT scan, that was found about 0.5 cm deep from the skin surface. Once removed, the lesion was examined by pathologists that described a tooth-like structure, with two roots and a partially resorbed crown (figure 3), surrounded by several haemorrhagic skin and subcutis fragments. The pieces were first fixed and, after the tooth decalcification, processed in paraffin.

Figure 3.

Tooth ‘extraction’.

Histopathological study of sections confirmed that it was a tooth with the evidence of well-developed dentin, cementum and pulp (figures 4 and 5). The surrounding tissue shows squamous, keratinising epithelium with chronic inflammation and dermal granulation tissue (figure 6). The specimen was also examined with Gram and Grocott stainings that excluded fungal or bacterial infections (figure 7). The enamel was non-visible probably because of the decalcification process.

Figure 4.

Fully developed pulp, dentin with a fine tubular substructure, cementum and normal periodontal ligament (H&E, original magnification at 1x).

Figure 5.

Details of the fine tubular structure of the formation (H&E, original magnification at 10x).

Figure 6.

Squamous, keratinising epithelium with acute, chronic inflammation and granulation tissue of derma surrounding the lesion (H&E, original magnification at 4x).

Figure 7.

Gram stainings negative for bacterial infections (H&E, original magnification at 40x).

Outcome and follow-up

The surgical access healed with no complications, and the sutures were removed after 10 days. At the 6 months control, physical examination did notify normal functionality and at the MRI, the right cheek did not show any sort of abnormality.

Discussion

The presence of an ectopic tooth is an exquisitely rare occasion. Odontogenesis is a complex process that normally involves the oral epithelium and the underlying mesenchymal tissue; teeth formation begins at the sixth week of embryonic life and is structured in phases that bring tooth buds to become fully structured teeth.⁵ In literature, few cases of ectopic teeth found in singular locations are described, such as maxillary sinus, palate, coronoid process and mandibular condyle.⁶ Even more rarely, the tooth formation is related to the presence of an odontogenic choristoma. This term was proposed by Noroozi and Arora¹ after the encounter and treatment of a 2-year-old boy with a tooth-like lesion in the cheek. The definition of choristoma consists of the presence of a tumour-like growth of a histologically normal, differentiated tissue in an ectopic position, as suggested by its greek etymological word choristos, which means separated; in histology, the word is used to refer to a histologically normal tissue that is present in an abnormal part of the body. This entity must be distinguished from teratoma, a tumour of germ cell origin presenting a variety of parenchymal cell types representative of more than one germ layer, usually all three (endodermal, mesodermal and ectodermal). Teratomas principally arise in the gonads but can occur rarely from sequestered primitive cell rests in other sites.⁷ They originate from totipotent cells that produce distinct type of tissues (ie, tooth structures, skin, hair follicles, sebaceous glands, smooth muscle, fat, cartilage, bone, neural structures and gastroenteric and respiratory epithelium^{8 9}). Regarding ectopic tooth formation, one plausible cause of the formation of a tooth outside of the mouth is related to the presence of pulp tissue that could be transplanted in early development and brought the formation of the tooth.¹⁰ In the presence of a hard structure of unknown nature, differential diagnosis first focuses on common causes, like post-traumatic bone or tooth displacement,¹¹ tissue infections¹² or tumour growth.¹³ In our case, the patient came to our attention for the skin lesion (figure 1) that appeared 3 months before. Due to the patient age, the skin lesion was also evaluated with dermatoscopy and the examination did not highlight any sign of skin malignancies. For further investigation, a CT scan was performed, showing a radiopaque structure embedded in a radiologically normal soft tissue of the cheek. Initially, differential diagnosis focused on more common causes like trauma-related foreign bodies or bone fragments, previous infections involving the maxilla or recent surgical procedures, but these options were excluded by the patient’s medical history and by the CT scan results that did not highlight any anomalies; however, during the patient history acquisition, the patient referred that since childhood an indolent, firm, hard tissue was palpable laterally to her nose and that she never worried about it due to the absence of growth or pain. To better establish the nature of the formation, it was decided to surgically remove the structure: the clinical and radiological differential diagnosis, the tooth-like shape but most importantly the histopathological features found by the pathologists brought the authors to the rare diagnosis of odontogenic choristoma that, due to the peculiar position and indolence, was discovered in such a late age.

Whether common or rare, the presence of intraoral or extraoral abnormalities is an everyday problem for the head and neck surgeon. Odontogenic choristoma is one of them; this peculiar pathological entity of unclear nature,² together with the broader family of choristomas, can clinically mimick a foreign body, the result of a trauma or a tumour, but once studied under the microscope, results in an interesting rare benign diagnosis with its own histological features that should be considered, even in the elderly patient, in the differential diagnoses of the head and neck neoplasms.

Learning points.

• Odontogenic choristoma is a rare encounter for the oro-maxillofacial surgeon, especially in late age.

• Patient history should be carefully obtained, in order to exclude traumatic or postinfective anomalies.

• In case of a displaced tooth-like formation without history of trauma or infections, odontogenic choristoma should be strongly considered in the differential diagnosis.

Ethics statements

Patient consent for publication

Obtained.