SALIVARY GLANDS
Nodular Oncocytic Hyperplasia (NOH), Oncocytoma, Oncocytic Cell Carcinoma (OCC)
These tumors are more common in the parotid and may be multifocal or bilateral. They occur more frequently in the 6th-8th decades of life. NOH and oncocytoma appear to be more frequent in females, but a review paper revealed a male to female ratio of 2:1 for OCC.
There are no identified risk factors, but a prior history of radiation exposure has been recognized in 20% of cases.
The most common clinical presentation is a painless slow-growing mass. However, pain and / or facial nerve paralysis may occur and are not criteria for malignancy.
Ultrasound is the first-line imaging method in the evaluation of salivary gland nodules. CT and MRI are useful for preoperative planning when the lesion is not appropriately visualized on ultrasound. They help in the assessment of the tumor extent, in the establishment of its relationship with the facial nerve, and in the exclusion of bone or deep soft tissue infiltration.
Due to a significant overlap of imaging findings among salivary gland tumors, cytology and biopsy are used to characterize lesions before surgery. However, cytology has a relatively low sensitivity (29%) in the detection of OCT. Furthermore, the distinction between oncocytoma and OCC is a histological diagnosis.
The treatment of choice is surgical resection with facial nerve preservation whenever possible. In OCC a more aggressive surgery may be necessary and some authors recommend adjuvant radiotherapy.
Oncocytomas can recur in about 20% of cases. The imaging appearance and prognosis of OCC is not well established due to their rarity. [2-5]
Warthin’s Tumor (WT)
WT corresponds to the second most frequent salivary gland tumor. It occurs more frequently in males in the 6th-7th decades of life. Usually, WT presents as slow-growing asymptomatic lesion and often it is multifocal and bilateral.
Imaging performance in accurately diagnosing this lesion is low, particularly when a single focus of tumor is found. Imaging features overlap with other salivary gland tumors, such as oncocytomas.
Fine-needle aspiration cytology (FNAC) is usually performed before surgery. Histopathological examination shows the presence of oncocytic cells without atypia mixed with polymorphonuclear lymphocytes and cellular debris.
Recurrence after surgery is very rare. Malignant degeneration has been described, however it is extremely rare. Therefore the prognosis is favorable. [6-8]
THYROID GLAND
Hürthle Cell Tumors (HCT)
HCT are composed of at least 75% of Hürthle cells (oncocytic follicular-derived cells). Females aged 52-62 years are more frequently affected. A relationship with prior radiation exposure was not established.
Previously HCT were considered a variant of follicular tumors. However, in the last WHO classification (2017) they are considered as a distinct entity, which comprehends benign (adenomas) and malignant (carcinomas) lesions. They can produce both high (> 500 ng/dL) or limited thyroglobulin levels and consequently, thyroglobulin may not be useful as a marker of post-surgical recurrence.
Ultrasound is the most useful imaging method for the evaluation of the thyroid gland. Literature shows scarce references about the ultrasound characteristics of HCT, which is explained by the relative rarity of these lesions. Since there are no specific ultrasound findings, diagnosis is not done based on imaging.
FNAC is indicated but does not allow prediction of the tumors’ behavior, which can only be determined on histopathological examination.
The approach is usually decided based on the risk factors for malignancy.
There are controversial data regarding the possible greater aggressiveness of Hürthle cell carcinoma compared to the other types of thyroid carcinomas, as well as a possible reduced response to radioactive iodine therapy. For these reasons, many clinicians choose to proceed to surgery, which can be more or less invasive also depending on intraoperative findings.
Differential diagnosis:
- Oncocytic variant of papillary carcinoma (a combination of oncocytic cytoplasm with nuclear characteristics of papillary carcinoma; its behavior does not appear to be significantly different from conventional papillary carcinoma).
- Oncocytic variant of medullary carcinoma (predominance of cells with oncocytic characteristics but associated with immunostaining positive for calcitonin; it seems to have a worse prognosis). [9-12]
ADRENAL GLANDS
Oncocytic Cell Adenoma / Carcinoma
Oncocytic cell adenoma and carcinoma are predominantly or exclusively composed of oncocytic cells. The adrenal glands are an unusual location for these tumors and there are scarce reported cases. They usually originate in the cortex and occur more frequently in the left adrenal gland. Cases in all age groups have been described, with an average age of incidence of 47 years, and females are more frequently affected than men. Since only a small percentage of these lesions are functionally active, the majority are detected incidentally.
OCT should be considered in the differential diagnosis of an indeterminate adrenal lesion. They are classified into three categories: benign oncocytoma; oncocytic tumor of uncertain behavior; and oncocytic carcinoma.
Imagiologically they are indistinguishable from other tumors and it is also not possible to determine whether they are benign or malignant.
Overall they present as bulky, round, well-circumscribed, encapsulated lesions. Whereas the dimensions of adrenal tumors typically help in distinguishing benign from malignant lesions, the dimensional criteria cannot be used with confidence in OCT. The reason for that is a significant overlap in the dimensions between benign and malignant tumors (from 2 to 20 cm and the average size is 8 cm). Hemorrhage and necrosis seem to be more frequent in malignant lesions.
Due to the tendency of OCT to be large, patients usually undergo surgery. The diagnosis is done in the histopathological examination and the prognosis is based on the Lin-Weiss-Bisceglia system criteria. [13-14]
KIDNEY
Oncocytoma
Renal oncocytomas originate from the intercalated cells of the cortical collecting duct. They correspond to 3-7% of all kidney tumors and may be sporadic or associated with Birt-Hogg-Dubé syndrome. In up to 16% of cases, they are multifocal and in up to 12% bilateral.
Oncocytomas are benign tumors with a predilection for males. Patients are usually asymptomatic but occasionally they may present with hematuria, pain, and a palpable mass.
Imaging features are variable.
The typical appearance is a homogeneous lesion with a central scar. However, oncocytomas may also be heterogeneous and in approximately 5-20% cystic changes or hemorrhage are seen. Calcifications are uncommon and when present they are usually within the central scar.
The wide spectrum of possible imaging features substantially overlaps those of renal cell carcinoma (RCC). The biopsy may suggest the diagnosis of oncocytoma, but there are cases of mischaracterized RCC or hybrid tumors. Consequently, although benign, renal oncocytomas are often surgically resected.
Differential diagnosis:
- Oncocytic variant of angiomyolipoma
- RCC (oncocytic variant of the papillary type; chromophobe type, particularly its oncocytic variant; these lesions usually exhibit indolent behavior)
- Hybrid tumor (oncocytoma coexisting with RCC in the same tumor, most commonly the chromophobe type; these lesions are also associated with a more indolent behavior). [15-20]