A rare case of iliac crest metastasis from acinic cell carcinoma of parotid gland

The patient was placed in the supine position and an ilioinguinal approach according to Letournel was performed [9]. The main incision began at the posterior portion of the iliac crest, then curved forward along the course of the iliac crest as far as the anterior superior iliac spine and ended about two fingerbreadths from the cranial side of the symphysis. This approach gives good exposure of the retroperitoneal space as well as the posterior retrogluteal area and permits a safe resection of the ilium. After transection of the skin and subcutis, the iliac crest was fully exposed subperiosteally. We observed a neoplastic contamination of the muscular tissues that surround the iliac crest. All of these tissues were excised and histologically analyzed. Then we proceeded with the resection of the infiltrated iliac crest (Type I pelvic resection according to the Enneking and Dunham classification [10]). The tissue resected was histologically analyzed. The iliac crest was reconstructed by pinning with two titanium wires (TEN) 3.0 mm in diameter in the distal margin and one in the proximal margin of the resection zone and using acrylic cement (Figures 6 and 7). The final histological report showed that the tissue from the salivary gland was neoplastic (dedifferentiated acinic cell carcinoma). The patient received adjuvant chemotherapy after surgery. A pelvic radiograph after 1 year showed there was good positioning of the metal wires and cement (Figure 8).

Acinic cell carcinomas are a type of uncommon salivary gland tumor, which were considered benign until 1953 when Buxton demonstrated their ability to metastasize and to recur locally [3]. Subsequently they were referred to as acinic cell carcinomas. They are considered, however, to be low-grade malignant tumors. This type of tumor recurs locally in 8.3% to 45% of cases and these recurrences may arise many years after the original diagnosis of cancer. In the literature there are reports of cases of local recurrence 30 years after the diagnosis of the primitive tumor [5]. As with other primary malignant parotid tumors, they rarely cause distant skeletal metastases [11]. They are found more frequently in the axial skeleton and especially in the thoracic spine [12‐14]. A new tumor entity of the salivary glands, mammary analogue secretory carcinoma (MASC) with ETV6-NTRK3 translocation, has recently been proposed. MASCs are classified as adenocarcinomas, not otherwise specified (ANOS) or acinic cell carcinomas (AciCC) by the current World Health Organization classification. MASCs can be differentiated from acinic cell carcinomas by a lack of periodic acid-Schiff diastase–positive zymogen granules and S-100 protein positivity. Immunohistochemically, the lesional cells of our patient were negative for S-100 protein and they contained Periodic Acid Schiff-positive secretory zymogen granules: hence the patient’s tumor was an acinic cell carcinoma.

The peculiarity of our case was the presence of a bone metastasis, originating from an acinic cell carcinoma of a parotid gland. It was in the right iliac crest in the appendicular skeleton. The pelvis is the second most common site of bone metastases after the spine, for this type of salivary gland tumor. Generally, this type of bone lesion shows through the onset of pain, mechanical instability due to extensive bone destruction and pathological fractures. For this reason, the goals in the treatment of these lesions are the control of pain, the prevention and treatment of fractures, maintaining the patient's independence and preventing progression of the tumor. Surgeons, radiotherapists, medical oncologists and pain clinicians should work together to improve the longevity and the quality of life of patients.

Lesions that do not involve the hip joint, such as those in the ischium, pubis or sacroiliac area, generally may be treated non-operatively [15, 16] with radiation alone or using minimally invasive procedures such as radiofrequency ablation, cryosurgery and/or percutaneous cementoplasty, following the technique proposed for acetabular metastasis [17].

The authors decided to reconstruct the iliac crest to avoid leaving a significant defect in the pelvic bone, which could cause pain at the donor site, instability of the pelvis [18], fractures of the ilium [19], donor site muscle herniation or abdominal content herniation [20]. Surgical indications for pelvic bone metastases are given by the Capanna and Campanacci Classification [21]. For our patient, the presence of a solitary metastasis, a primitive tumor with good prognosis (acinic cell carcinoma), 3 years since detection of the primary tumor (Class 1 of the Capanna and Campanacci Classification) and considering the specific clinical case (young patient, pain resistant to medical treatment), the surgical technique chosen was a resection with wide surgical margins, following the Enneking and Dunham Classification (P1), with reconstruction using acrylic cement and TEN.