This case highlights unusual histopathological findings in a well-defined hypodense interproximal and palatal lesion of the anterior maxillary teeth, initially diagnosed as “a hair-producing cyst of an undetermined origin”. In typical clinical scenarios, the differential diagnoses for well-defined periradicular or interradicular lesions include endodontic and non-endodontic pathoses. Among non-endodontic lesions, the most common entities are odontogenic keratocyst and nasopalatine duct cyst [9]. In the present case, the hypodense lesion involved the interproximal region of the anterior maxillary teeth, extended to the palatal aspect, and demonstrated a possibility of connection and loss of nasopalatine canal cortication (Fig. 1). Based on these radiographic and clinical findings, odontogenic keratocyst (OKC), nasopalatine duct cyst (NPDC), lateral periodontal cyst (LPC), and other benign odontogenic tumors, such as ameloblastoma and central odontogenic fibroma, were considered. However, given to the intraoperative findings during excisional biopsy, it revealed hair structures within the cyst-like cavity—an uncommon feature in such lesions. This unexpected observation prompted consideration of rare diagnoses, including intraosseous epidermal inclusion cyst [10, 11] and dermoid cyst [12]. Although no prior reports of intraosseous teratoma of the jaw bones exist, teratomas involving other bones have been documented and could also be considered as a differential diagnosis in this case [13, 14].

Histologically, the specimen consisted of fragments of variably dense fibrocollagenous connective tissue with prominent acute and chronic inflammatory infiltrates. Within the reactive connective tissue, terminal hair shafts associated with a foreign body–type multinucleated giant cell reaction were identified. Focal fragments of non-keratinizing squamous epithelium were also observed (Fig. 2). The histopathological features of OKC, NPDC, LPC, and other odontogenic tumors in the original differential diagnoses were not present. Although terminal hair and fragments of epithelial lining were observed, other features of cysts/tumors known to produce hairs were also not seen. Instead, the findings were most consistent with a foreign body reaction to hair, characterized by dense acute and chronic inflammation with multinucleated giant cell response. On this basis, an initial diagnosis of a “hair-producing cyst of undetermined origin” was rendered. Given the unusual and previously unreported nature of this entity, the oral pathologists requested that the clinician re-evaluate the patient’s history and re-examined to investigate potential sources of hair within the lesion, in order to achieve an appropriate clinico-pathological correlation.

It is extremely rare and unusual to observe heterotopic hair growth within oral cavity. As reported in most previous studies, the etiology of such occurrences remains unclear. Some authors have proposed that this phenomenon may result from aberrant embryonic fusion of ectodermal tissues or developmental defects [3,4,5,6,7]. Table 1 summarizes the reported cases of heterotopic hair growth in the oral cavity. As shown in the table, one report described hair overgrowth arising from a previous skin graft at a surgical site. Therefore, it is critical to rule out any prior history of palatal or oral surgery, including skin grafting procedures, that might account for intraoral hair growth [8], as well as history of orofacial trauma that could have introduced hair follicles or skin appendages into the oral cavity.

However, in the present case, the patient denied any history of trauma, prior surgery, or procedures that could account for these findings. Interestingly, she instead reported a history of trichotillomania, characterized by habitual hair pulling and plucking. She admitted to occasionally placing the pulled hairs in her mouth, chewing or nibbling on them, and pressing them into the palatal site. She also exhibited a relatively deep bite, which may have facilitated this habit, leading to trapping of hairs in the palatal region, the subsequent development of a periapical lesion involving teeth #9 and #10, and eventually the formation of a sinus track opening on the facial aspect, corresponding to her chief complaint. She further stated that although she had controlled her trichotillomania for many years, the habit has returned about 18 months previously following the loss of a household member. This behavioral pattern provides a plausible explanation for how hair became entrapped at the site over time.

Given these clinical and behavioral findings, the most likely pathogenesis involves repeated mechanical irritation and microtrauma to the oral mucosa, allowing hair fragments to penetrate and become embedded in the soft tissue. These foreign materials subsequently triggered localized, persistent acute and chronic inflammatory responses. Over time, the inflammation may have contributed to focal osteolysis of the underlying bone, creating a pathway for hair to migrate into the intraosseous compartment. Once within the bone, the retained hair acted as a persistent foreign body, perpetuating inflammation. As a consequence, a foreign body reaction developed, characterized by localized acute and chronic inflammation and fibrous encapsulation around the hair, which ultimately resulted in the formation of a cystic lesion [15, 16].

To our knowledge, this is the first reported case of intraosseous hair entrapment resulting in a hair-induced cyst-like entity as a localized foreign body reaction. Previous reports have primarily described soft tissue involvement, either following surgical reconstruction with skin grafts [8], the possible association with alopecia areata [7], high circulating testosterone in polycystic ovary syndrome [17], or as lesions of undetermined origin in the buccal mucosa, tongue, or gingiva [3,4,5,6,7, 18]. In conclusion, we report a rare case of an intraosseous hair-induced cyst-like entity in the anterior maxilla. This case also emphasizes the significance of anamnesis in determining possible etiology of rare entities. In this case, trichotillomania was identified as a potential contributing factor to the development of the lesion.