Primary aneurysmal bone cysts involving the mandibular condyle are exceedingly rare and may present unique difficulties with respect to diagnosis, ablation and reconstruction. A 27-year-old male Jehovah’s Witness presented to an emergency department following a minor traumatic incident with left-sided facial swelling, paresthesia of the third division of the left trigeminal nerve and trismus. A diagnosis of a central giant cell lesion was rendered from an incisional biopsy of a lesion involving the left mandibular condylar head. The patient was initially treated by curettage and installation of a stock temporomandibular joint prosthesis. Histopathologic and molecular analysis revealed the presence of a primary aneurysmal bone cyst. The patient was lost to follow up and eventually returned with severe trismus secondary to ankylosis between a mass of heterotopic bone circumscribing the left mandibular condylar prosthesis and temporal bone which required pre-operative embolization, resection of the osseous mass and placement of a custom temporomandibular joint prosthesis. Intraoperatively, the coil within internal maxillary artery was encountered. Recurrent foci of aneurysmal bone cyst was noted within the resection specimen which was not evident upon pre-operative imaging. This report highlights the utility of multidisciplinary care and the application of contemporary technologies and procedures in the context of a staged approach to temporomandibular joint reconstruction for the treatment of a rare neoplasm in a unique patient population.
The primary ABC is a rare lesion that may present complex management decisions.
The diagnostic features of primary ABCs overlap with other giant cell lesions.
Accurate identification of primary ABCs is essential for appropriate management.
Staged approaches to TMJ TJR are cost-efficient and facilitate interim function.
Embolization prior to TMJ ankylosis surgery reduces peri-operative blood loss.
The primary aneurysmal bone cyst (ABC) is a benign osteolytic giant cell lesion that was previously considered a non-neoplastic cyst [ ]. Recent molecular studies have identified multiple molecular translocations responsible for the pathogenesis of this entity, supporting the neoplastic nature of primary ABCs which typically present as rapidly expanding intra-osseous lesions [ ]. ABCs represent only 2% of all primary bone tumours, with a mere 1.5% of all cases developing within the gnathic complex [ ].
The contemporary mainstay of imaging for ABCs is multi-detector computed tomography (MDCT), which is often preceded by plain film radiographic evaluation. Unfortunately, the radiologic appearance of ABCs is heterogenous, sharing features that are often observed in other lesions involving the gnathic complex [ ]. The presence of cystic spaces with fluid levels, while helpful in developing a differential diagnosis, are non-pathognomonic, as a myriad of other lesions, both benign and malignant, may also demonstrate this feature which may ultimately be obscured secondary to technical limitations during image acquisition and viewing [ ].
Histologically, ABCs are generally well-circumscribed and demonstrate cystic blood-filled spaces lined by fibrous septae [ ]. The fibrous component is composed of bland fibroblasts with scattered osteoclast-type giant cells and reactive woven bone may be present with osteoblastic rimming. Primary ABCs bear similar histological features to the central giant cell granuloma, giant cell tumor of bone and fibroma of tendon sheath, which are all known to occur in the craniofacial complex [ , ]. Therefore, clinical and radiographic correlation may still be insufficient for definitive diagnosis of giant cell lesions involving the gnathic structures.
Management of gnathic ABCs has been achieved through en bloc resection, curettage, embolization and radiotherapy, with recurrence rates between 0% and 50% [ ]. The selection of a particular treatment modality is dependent on the fine balance between the risk of recurrence and morbidity associated with the selected treatment [ ]. This report highlights the ablative and reconstructive factors associated with the treatment of a primary ABC involving the mandibular condyle. Several pre-operative considerations involving the use of contemporary technologies, adjunct procedures and a staged approach for mandibular reconstruction were required due to the non-specific initial working diagnosis and patient’s religious beliefs which precluded delivery of blood products.
Presentation of case
A 27-year-old male patient with a past medical history of hypothyroidism, schizophrenia and depression presented to our tertiary care facility endorsing a two-week history of trismus and left-sided paresthesia involving CN V 3 , as well as a three-year history of left-sided facial asymmetry following minor left-sided facial trauma. Clinical examination revealed a maximum interincisal opening (MIO) of 20 mm, paresthesia involving the left lower lip and a firm, non-painful left preauricular swelling. Panoramic and MDCT imaging ( Fig. 1 a–c) revealed a relatively well-defined and expansile lesion involving the left mandibular condyle suggestive of a giant cell lesion. A central giant cell lesion was diagnosed based on an incisional biopsy ( Fig. 1 d) and all pre-operative laboratory tests, including serum calcium and parathyroid hormone, were within the range of normal.
Informed consent was subsequently obtained for lesion excision and installation of a stock temporomandibular joint (TMJ) prosthesis under general anesthesia. The patient identified as a Jehovah’s Witness and did not consent to the use of blood products. Following the induction of general anesthesia and placement of the patient in maxillomandibular fixation (MMF), exposure of the lesion was achieved through a modified Blair incision ( Fig. 2 a). An osteotomy was created through the left mandibular ramus superior to the mandibular foramen ( Fig. 2 b) and the lesion was delivered in multiple fragments ( Fig. 2 c) up to the level of the TMJ disc which was left in situ . A reconstruction plate (Zimmer Biomet) and stock condylar prosthesis (Lorenz) were then installed ( Fig. 2 d), MMF released to confirm occlusion and the operative site closed. At the time of discharge on post-operative day (POD) 3, minor directional sensation deficits of CN V 3 , normal function of CN VII and a stable occlusion were observed. Histopathologic ( Fig. 1 e) and ubiquitin specific peptidase 6 (USP6) fluorescence in situ hybridization (FISH) examination confirmed the diagnosis of a primary ABC.