Orbitofrontal cholesterol granuloma masquerading as frontal sinus mucoceles: report of two cases

Orbital cholesterol granuloma is a relatively rare condition caused by a foreign body reaction against cholesterol crystals. It predominantly occurs in young or middle-aged men [1]. The orbitofrontal cholesterol granuloma was initially described in 1902 by Denig [2, 3]. Other terms such as lipid granuloma, cholesteatoma, chronic haematic cyst, xanthomatosis, and histiocytic granuloma are also used for orbital cholesterol granuloma. However, these terms are inaccurate, and cholesterol granuloma is the most appropriate [1]. However, histopathology confirmed that the mass contained cholesterol crystals, fibrous envelope, hemosiderin, granuloma, and other components, but the pathogenesis of cholesterol granuloma is still unclear. In the petrous, the pathogenesis is believed to be caused by ventilatory obstruction of the pneumatized temporal bone resulting in local tissue breakdown and deposition of cholesterol which then crystallizes and stimulates a granulomatous reaction [5]. However, this mechanism does not apply to orbital cholesterol granuloma. In orbit, orbital hemorrhage of any cause, such as minor trauma, or spontaneous bleeding in an anticoagulant-treated patient, is the initiating event for cholesterol granuloma formation [5]. Blood-derived products degrade cholesterol and deposit crystals that stimulate the growth of surrounding tissue to form granulomas [6, 7]. Nevertheless, only a minority of cases have a history of trauma [8]. Moreover, neither of the two patients reported in this study had a history of trauma. It was speculated that a very mild trauma may have occurred inadvertently. Spontaneous bleeding caused by abnormal coagulation or blood vessel development could be one of the possibilities [9].

Cholesterol granuloma may arise within the diploe of frontal bone [10], enlarge and erode through the outer table of the bone to extraperiosteal space above the lacrimal fossa. The lesion causes ophthalmological symptoms of upper eyelid swelling, ptosis, ocular distention, proptosis, hypoglobus, extraocular movement restriction, and diplopia. The typical features observed on CT are a well-defined lesion in the superolateral orbit, isodense with the brain, and extensive erosion adjacent to the frontal bone and lacrimal fossa. The typical findings on contrast-enhanced imaging are a non-enhancing mass that presented predominantly hyperintense and heterogeneous on both T1WI and T2WI, whereas the hyperintense signal is characteristic of chronic bleeding. The paramagnetic effect of haem iron (Fe3+) in methemoglobin results in the characteristic high signal on all images reflecting a shortening of the T1WI involved tissue and a lengthening of the T2WI [1].

Orbitofrontal cholesterol granuloma is rare, has a prediliction to the frontal sinuses. The location of disease is similar to the frontal sinus mucoceles. Therefore, the two patients were misdiagnosed before surgery and should be differentiated from them. Mucoceles are expansive cysts of mucus secreted by goblet cells interspersed in the ciliated mucosa [11]. Although all paranasal sinuses are susceptible, the frontal and ethmoidal sinuses have the highest incidence [11]. They can occur at any age, but most patients with mucoceles are between 40- 60 [12,13,14]. Compromised sinus ventilation is the basic etiology of mucocele formation [13, 15]. The reasons may include (1) lesions of the nasal cavity and sinuses (or abnormal development), such as nasal polyps, sinus osteoma, and nasal septum deviation, and (2) inflammation or trauma leading to nasal adhesion and sinus obstruction [16]. Mucoceles can compress and erode the surrounding bone wall, leading to absorption of the orbital wall as they grow gradually [11, 17]. Frontal sinus mucoceles frequently lead to the absorption of superior orbital wall, extending into the orbit, resulting in ocular symptoms and signs. The ocular manifestations are similar to orbital cholesterol granuloma. CT scan shows expansive growth of the mucoceles in the sinuses with absorption and destruction of adjacent bone and intrusion into surrounding structures. The clear boundary; the internal density is more uniform, mostly low density; a few can be equal or even high density. The density is dependent on the protein concentration of sac fluid. When protein concentration is high, density is high, whereas when protein concentration is low, density is low. Mucocele MRI signal intensity is quite distinct, and signal level may correlate with disease duration. Subsequently, patients with a short disease course have more moisture and hypointense presentation on T1WI. Patient with a long period of the disease has more protein, presenting hyperintense on T1WI [18].

The mainstay of treatment for cholesterol granuloma is surgical resection with curettage of the abnormal bone to reduce the recurrence of disease. Cholesterol granuloma has typical histopathological features with cholesterol clefts, multinucleated giant cells, histiocytes, foamy macrophages, fiber textures, altered blood pigments, and calcifications.

In conclusion, orbital cholesterol granuloma is relatively rare, has a prediliction to the frontal sinuses. Suppose the orbital CT shows a similar cystic lesion with irregular bone destruction in the superolateral orbit. In that case, MRI displays that the lesions are hyperintense signals on T1WI and T2WI, and the contrast-enhanced imaging reveals that most of the tumors are not significantly enhanced. The diagnosis of orbitofrontal cholesterol granuloma should be considered.

留言 (0)

沒有登入
gif