**4.3 Definitive diagnosis**

*Rhinosinusitis*

literatures.

be a primary neoplasm [10].

from 11 months to 20 years [3].

**4.1 Clinical presentation**

**4.2 Radiological diagnosis**

**3.7 Other associated bone pathologies**

granuloma, fibrous dysplasia, and fibromyxomas [1, 11, 12].

**4. Aneurysmal bone cyst in sino-nasal region**

**3.5 The origin of aneurysmal bone cyst**

**3.6 The pathogenesis of aneurysmal bone cyst**

ABC typically originated from the long bones. It represents 1–2% of all primary

ABC's pathogenesis is obscure. Historically, it was believed that ABC resulted

ABC is generally solitary and thought to arise as primary neoplasm as a result of translocation. On the other hand, ABCs may be found as secondary lesions, in the presence of other benign bone lesions such as non-ossifying fibroma, giant-cell

ABC's involvement of ethmoid sinuses is extremely rare [4]. Only 13 such cases of involvement of ethmoid sinuses were reported in the English literatures. The mean age at debut in ethmoid ABCs is around 11.6 years with patient age ranging

The diagnosis of an ABC from clinical aspect can be challenging with variable clinical presentation. Clinical presentation is highly dependent on the location of the ABC. The most common presentation of ABC in sino-nasal region relates to the presence of the expansile sockets against lamina papyracea [13]. The patient can be presented with nasal obstruction and/or facial heaviness. Epistaxis is a relatively rare presentation, since it has been reported in literatures in only two cases [3]. In the review by Hnenny et al. [14], they report that lesions affecting the skull base are more likely to present with neurologi-

cal deficits including anosmia, ataxia, otalgia, facial numbness, and hearing loss.

and to plan the surgical procedure needed. ABC demonstrates the presence of

Imaging studies, namely, CT scan and MRI, are essential to help with diagnosis

from increased venous pressure that is causing extravasation of cellular and blood contents into cyst-like voids in the bone [3]. More recent work showed that identification of a genetic driver—a translocation-induced upregulation of the ubiquitin-specific protease USP6 (Tre2) gene—defined at least a subset of ABCs to

tumors of the bone, occurring primarily in the metaphysis of long bones and vertebrae [8]. The ABC lesions typically involve long tubular bones. Between 3 and 12% of ABCs are found in the head and neck where they most commonly arise in the mandible or maxilla [3, 4]. Guida et al. [9] report that lesions involving the skull comprise 3–6% of all ABCs. Very few have ever been reported in the paranasal sinuses and are exceptionally rare in the pediatric population. Although they have been reported in the maxilla, mandible, cranium, orbital roof, temporal bone, and sphenoid bone, involvement of ethmoid sinuses as in our case is extremely rare [4]. Only 13 such cases of involvement of ethmoid sinuses were reported in the English

**94**

Despite all the imaging appearances suggestive of ABC, histological confirmation is essential for diagnosis. Histological evaluation of the suspected lesion is mandatory for diagnosing ABCs accurately. Ultimately, histological evaluation is key, and ABCs typically demonstrate irregular, blood-filled chambers with islands of bone and fibrous tissue [17]. In gross appearance, ABCs are spongy, hemorrhagic masses covered by a thin shell of the reactive bone. Microscopically, ABCs showed abundant red blood cells with pale brown hemosiderin that is filling cyst-like spaces and bounded by septal proliferations of fibroblasts, with mitotically active spindle cells, osteoid, calcifications, and scattered multinucleated giant cells [18]. The principal diagnostic error occurs if the histologist fails to appreciate the lining of the blood-filled spaces [2].
