bubble_chart Overview

Adenoid cystic carcinoma, also known as cylindroma or adeno-carcinoma of cylindroma type, was first reported by Billroth and referred to as cylindroma. Most believe the tumor originates from the salivary gland ducts, but it may also arise from the basal cells of the oral mucosa.

bubble_chart Pathological Changes

(1) Gross Morphology The tumor is round or nodular in shape, varying in size but mostly measuring 2–4 cm in diameter, with indistinct boundaries from surrounding tissues. The mass is typically solid, slightly firm in texture, and lacks a capsule. The cut surface appears grayish-white or pale yellow, moist, with some areas showing tiny cystic cavities, while a few cases are dominated by larger cysts.

(2) Microscopic Examination The tumor consists of two types of cells: duct-lining epithelial cells and myoepithelial cells. The tumor cells exhibit various arrangements, with the cribriform structure being the typical pattern. The cells form round, oval, or irregular epithelial clusters containing numerous round or oval cystic spaces of varying sizes, resembling a sieve-like appearance, similar to the cross-section of a lotus rhizome node. These small cystic spaces are often surrounded by neoplastic myoepithelial cells and contain mucoid material. Under electron microscopy, the lumens contain basement membrane, stellate granular mucoid substances, and collagen fibers, among which the collagen fibrils may become hyalinized, even occupying the entire cystic cavity and forming hyaline cylinders.

In adenoid cystic carcinoma, besides the cribriform pattern, tumor cells may also arrange densely into small solid cords, clusters, or duct-like structures. The duct-like structures are formed by 2–3 layers of cells, sometimes containing red-stained mucus in the lumen. The solid variant of adenoid cystic carcinoma is less common, often presenting as partially large solid clusters mixed with cribriform or cord-like patterns, with central areas of cellular degeneration, necrosis, and cystic changes in larger clusters.

(3) Biological Characteristics Although adenoid cystic carcinoma grows slowly, it lacks a capsule and is highly invasive, with infiltration often extending beyond the grossly visible tumor margins during surgery, leading to a high recurrence rate postoperatively. The tumor has a tendency to grow along or around fibrous tissues, enabling it to spread along nerves, invade the nerve sheath and fiber bundles, and cause neurological symptoms. It may also grow along or around blood vessels, impairing vascular contractility and leading to bleeding during surgery. The tumor can further spread along blood vessels, nerves, and collagen fibers to adjacent glandular and other tissues. In advanced stages, tumor cells readily invade blood vessels, resulting in hematogenous metastasis. According to Spiro, the distant metastasis rate is 43%, commonly involving the lungs, liver, and bones, while lymphatic metastasis is rare.

bubble_chart Clinical Manifestations

Adenoid cystic carcinoma accounts for 5–10% of salivary gland tumors and 24% of malignant salivary gland tumors. It commonly occurs in the salivary glands, with the palate glands being the most frequent site. Although less common in the major salivary glands, it is a prevalent tumor in the submandibular and sublingual glands. It constitutes only 2–3% of parotid gland tumors. Eeroth reported 2,513 cases of salivary gland tumors, including 119 cases of adenoid cystic carcinoma, with 49 cases occurring in the parotid gland (2% of parotid tumors), 26 cases in the submandibular gland (16% of submandibular tumors), and 44 cases in the minor salivary glands of the palate (24% of palatal salivary tumors). In a domestic report by Cheng Jun involving 225 cases, 162 occurred in the minor salivary glands, with 87 cases (38.7%) in the palate, and 63 cases in the major salivary glands. There is no significant gender difference in incidence, though females may be slightly more affected. The most common age range is 40–60 years.

In the early stages, the tumor often presents as a painless mass, though a few cases exhibit pain at discovery, which may be intermittent or continuous. The pain can range from mild to severe. The disease course is prolonged, lasting months or years. The tumor is generally small, mostly 1–3 cm, though some can be larger. The mass may resemble a mixed tumor in shape and characteristics, appearing round or nodular with a smooth surface. Most masses have indistinct borders, limited mobility, and some may be fixed or adherent to surrounding tissues. The tumor frequently spreads along nerves. Adenoid cystic carcinoma in the parotid gland often leads to facial nerve paralysis and can extend along the facial nerve to involve the mastoid and temporal bones. In the submandibular or sublingual glands, it may spread along the lingual or hypoglossal nerves to distant sites, causing sensory and motor disturbances in the tongue. Palatal adenoid cystic carcinoma can extend along the maxillary nerve into the cranial cavity, destroying the skull base and causing severe pain. The tumor also often invades adjacent bone, such as the mandible in submandibular or sublingual gland cases, or the palatine bone in palatal cases. When adenoid cystic carcinoma in the minor salivary glands involves the mucosa, aside from a hard, nodular mass, prominent reticular dilated capillaries are often visible. Patients generally show no significant systemic symptoms unless complications arise in advanced stages, worsening the condition.

bubble_chart Diagnosis

Adenoid cystic carcinoma, like other types of malignant salivary gland tumors, presents a diagnostic challenge preoperatively. For salivary gland masses that exhibit early pain and nerve paralysis, adenoid cystic carcinoma should be the primary consideration. To confirm the diagnosis, fine-needle aspiration cytology can be performed. Microscopic examination reveals tumor cells that are round or oval, resembling basal cells, and arranged in spherical clusters. Mucin forms spherical masses surrounded by one or more layers of tumor cells. This distinctive feature is absent in other salivary gland epithelial tumors and can be used to diagnose adenoid cystic carcinoma. Accurately determining the extent of adenoid cystic carcinoma involvement is also difficult. Current diagnostic methods, such as sialography, X-ray, B-mode ultrasound, CT, and radionuclide scanning, cannot fully address this issue.

bubble_chart Treatment Measures

Surgical resection remains the primary treatment for adenoid cystic carcinoma. The main principle for radical treatment of adenoid cystic carcinoma is extensive local excision. That is, when functional impact is minimal, surrounding tissues should be removed as much as possible, even sacrificing some organs that appear normal to the naked eye. For nerves adjacent to the tumor, tracking excision should be performed as much as possible. Intraoperative frozen section examination should be used to check whether the margins are normal. In principle, total parotidectomy should be performed for adenoid cystic carcinoma. Considering the high neural invasiveness of adenoid cystic carcinoma, excessive consideration should not be given to preserving the facial nerve. For submandibular gland cases, at least submandibular triangle dissection should be performed. For palatal cases, subtotal or total maxillectomy should be considered. If the greater palatine foramen is involved, the pterygopalatine canal should be excised along with the pterygoid plate, and skull base resection may be performed if necessary.

The cervical lymph node metastasis rate of adenoid cystic carcinoma is about 10%, but direct invasion is far more common than tumor emboli metastasis. Allen and Bosch, through their study of regional lymph node metastasis in adenoid cystic carcinoma, concluded that so-called lymph node metastases are all cases where the tumor directly grows into the lymph nodes, with tumor cell infiltration in the surrounding soft tissues, and no cases of tumor emboli metastasis were observed. Therefore, selective lymph node dissection is not necessary for adenoid cystic carcinoma patients.

For recurrent or advanced stage tumors, in addition to extensive resection, radiotherapy can be combined during treatment. When complete surgical removal is not possible in some anatomical locations, postoperative radiotherapy is also required. Combining surgery with radiotherapy may reduce the recurrence rate. For some cases where surgery is not an option, radiotherapy can also be used to control progression. Previously, it was believed that salivary gland malignancies were resistant to radiation, but recent research results indicate that adenoid cystic carcinoma is sensitive to radiation, although radiotherapy alone cannot completely cure it.

Advanced stage patients or postoperative recurrence patients can also be treated with chemotherapy to reduce recurrence. Chemotherapy is mainly used in combination with surgical treatment or palliative care. According to reports by Skibba and Bueld, combination chemotherapy using cyclophosphamide, vincristine, 5-FU, doxorubicin, and mitomycin can sometimes completely eliminate metastatic lesions. Among single-agent therapies, cisplatin is the most effective, with a response rate of 37.05%.

bubble_chart Prognosis

The site of the lesion, tumor size, and whether the surgical resection was complete are directly related to the prognosis. Adenoid cystic carcinoma is prone to local recurrence, and multiple recurrences often lead to distant metastasis. The primary causes of death are local destruction or distant metastasis. The tumor progresses slowly, and even with recurrence, patients can survive for many years with the tumor. Many scholars believe that the prognosis of adenoid cystic carcinoma should be assessed over a 10-year period. According to Spiro's report on 242 cases of adenoid cystic carcinoma in major and minor salivary glands, the 5-, 10-, 15-, and 20-year survival rates were 63%, 39%, 26%, and 21%, respectively. In a domestic report by Ma Daquan, the 5-, 10-, and 15-year survival rates were 64.4%, 36.7%, and 14.3%, respectively. The prognosis also varies depending on the site of occurrence. Tumors in the parotid gland have a better prognosis, followed by minor salivary glands, while those in the submandibular gland, nasal cavity, and paranasal sinuses have the worst prognosis. Spiro's report on 242 cases showed 10-year cure rates of 29% for the parotid gland, 23% for minor salivary glands in the oral cavity, 10% for the submandibular gland, and only 7% for the nasal cavity and paranasal sinuses.