Lipomas are the most common benign mesenchymal tumors [1]. They are usually presenting as subcutaneous neoplasms of mature adipocyte cells. However, they can occur wherever fatty tissue is found. In 80% of cases, they are typically subcutaneous lipomas with no particularities [1, 2]. Head and neck lipomas count for 13% of all cases, mainly located in the nuchal area [6]; less frequently in the anterior cervical region, infratemporal fossa, oral cavity, and parotid gland; and even more rarely in the upper aerodigestive tract [5]. In our case, the lipoma originated from the anterior wall of the left pyriform sinus.

Lipomas are usually described as painless, slow-growing soft tissue tumors of different sizes that are characterized by an insidious evolution. In fact, they usually remain silent and are often discovered fortuitously during a clinical examination or a radiology test. Nevertheless, lipomas of the upper aerodigestive tract may go unnoticed on CT scans due to the similarity of density between the air and the fatty portion especially in the pedunculated forms. They are most often sporadic in isolated cases. However, in 5–15% of patients, lipomas are multiple, thus described as lipomatosis, and approximately a third of these will be familial [7] as well as associated with other syndromes and diseases such as Gardner’s syndrome, Bannayan-Zonana syndrome, Dercum syndrome, Cowden syndrome, Proteus syndrome, and Madelung’s disease [8].

Clinically, lipomas may remain asymptomatic for a long period until reaching a considerate size; consequently, they are discovered at an advanced stage. On the other hand, for the symptomatic forms, and more precisely in the pharyngeal ones, clinical features depend on the location and the impact of these lipomas on the adjacent structures. The patient may describe a simple throat discomfort, a pharyngeal foreign body sensation or heaviness, dysphagia, and swallowing difficulty. Furthermore, some may experience life-threatening dyspnea, especially in the pedunculated forms, due to laryngeal obstruction, a complete externalization through the oropharynx as the case described by Gilberto et al. [9], or in the huge compressive forms. In this context, one case of death has been reported following asphyxia which was secondary to a voluminous and obstructive hypopharyngeal lipoma [10]. On the optic endoscopy, the lipoma appears as a well-limited, round-shaped, submucosal mass. It may be pedunculated or sessile.

Histologically, simple lipomas can be distinguished, based on their stroma, from the other benign variants including myolipoma, chondrolipoma, angiomyolipoma, adenolipoma, myxolipoma, and spindle cell lipoma [11] on the one hand. On the other hand, it is also important to rule out some malignant histology types such as liposarcoma in particular the well-differentiated cell form [12].

Concerning radiology features, lipoma is typically a well-circumscribed, round-shaped mass with homogeneous characteristics corresponding to a fat imaging with a thin capsule, very thin septa (< 2 mm), and some scattered small areas of soft tissue density. On ultrasounds, they are mostly isoechoic (28–60%) and hyperechoic (20–50%), yet they are hypoechoic in about 20% of the time [1] with no acoustic shadowing and no or minimal color Doppler flow [13]. If encapsulated, the capsule may be difficult to identify sometimes and to be distinguished from the air around in the pharyngolaryngeal area [7]. Calcification may also be present in up to 11% of cases, although more commonly associated with well-differentiated liposarcoma [7]. Moreover, avidly enhancing, thick/nodular septa or evidence of local invasion in addition to heterogeneous echotexture, more than minimal color Doppler flow, suggests malignancy.

The diagnosis is usually indicated by clinical features and ultrasound results. However, in the upper aerodigestive tract, CT scan and MRI imaging may be helpful for a better evaluation of the mass and the surrounding structures. On CT scan, lipomas presented as fatty, homogeneous, low-attenuation masses with minimal internal soft tissue component occasionally. It may also show some areas of fat necrosis, blood vessels, and muscle fibers whereas a liposarcoma is eliminated firstly [7]. MRI can also be used as a diagnosis tool and show a high-signal mass on both T1 and T2 with saturation on fat-saturated sequences. In fact, MRI represents the main imaging tool for lipoma diagnosis with or without atypical features. As a matter of fact, when no suspicious features are present, MRI is 100% specific regarding the diagnosis of lipoma [14]. In the opposite case, if suspicious features of malignancy are present, the specificity of MRI is lower since some masses with atypical features will nonetheless be simple lipomas, while the sensitivity is still 100% [14].

Well-differentiated liposarcomas, which represent the main and most dangerous differential diagnosis of lipomas, have high chances of local recurrence and a possibility of delayed dedifferentiation after the initial treatment [15]. Because of the differences not only in the treatment’s modalities, but also concerning the prognosis and the follow-up protocols, it is very important to distinguish simple lipomas from well-differentiated liposarcomas. In fact, immunohistochemistry describes the liposarcoma subtypes disclosing different morphologies, genetics, clinical behavior, pattern of disease progression, response to treatment, and 5-year survival rate [15, 16].

In the upper aerodigestive tract, surgical management presents a challenge regarding the security of the upper airways, the possibility of intubation, the possibility of jet ventilation use, and endoscopic surgery sittings. Since this is a rare entity, each case should be considered unique and have to be managed individually. Nonetheless, it seems that hypopharyngeal lipomas tend to rise from the post-cricoid region [15, 16]. Therefore, securing the upper airways might be challenging if the tumor is large and has no peduncle which implies a transitory tracheostomy. Also, the lent of the peduncle base might condition the necessity or not to put mucosal sutures or surgical glue in order to prevent salivary fistula. Surgical excision might be performed using endoscopic cold instruments (micro scissors, sickle). However, CO2 laser offers better ergonomics especially regarding bleeding control.

Table 1 summarizes all hypopharyngeal lipomas reported in the literature to date.

Table 1 Chart summarizes all hypopharyngeal lipomas reported in the literature to date

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