# Surgical Anatomy and Pathology of the Major Salivary Glands

## Introduction

The major salivary glands -- parotid, submandibular, and sublingual -- are frequent sites of pathology encountered by the OMFS surgeon. A thorough understanding of the surgical anatomy, including the intimate relationship of the facial nerve to the parotid gland, is essential for safe surgical intervention. This lecture reviews the anatomy, common pathologic conditions, and diagnostic approach to salivary gland disease.

## Anatomy of the Major Salivary Glands

| Gland | Size | Secretion Type | Duct | Duct Opening | Key Nerve at Risk |
|---|---|---|---|---|---|
| Parotid | Largest | Serous | Stensen's | Opposite maxillary 2nd molar | Facial nerve (CN VII) |
| Submandibular | Intermediate | Mixed (serous + mucous) | Wharton's | Sublingual caruncle | Marginal mandibular (VII), lingual nerve |
| Sublingual | Smallest | Mucous | Ducts of Rivinus (+ Bartholin's) | Sublingual fold | Lingual nerve |

### Parotid Gland

The parotid is the largest salivary gland and produces predominantly serous secretion. It is located superficial to the masseter muscle and ramus of the mandible, enclosed within the parotid fascia (derived from the superficial layer of deep cervical fascia). Stensen's duct exits the anterior border, crosses the masseter, pierces the buccinator, and opens opposite the maxillary second molar. The facial nerve (CN VII) traverses the gland, effectively dividing it into superficial and deep lobes. The nerve enters the gland after exiting the stylomastoid foramen, divides into temporofacial and cervicofacial trunks, and gives off five terminal branches: temporal, zygomatic, buccal, marginal mandibular, and cervical. The retromandibular vein and external carotid artery also traverse the gland. The auriculotemporal nerve (CN V3) provides parasympathetic secretomotor fibers via the otic ganglion.

### Submandibular Gland

The submandibular gland is a mixed serous and mucous gland that produces approximately 70% of resting saliva. It is located in the submandibular triangle (digastric triangle), superficial to the mylohyoid muscle, with its deep lobe wrapping around the posterior free edge of the mylohyoid. Wharton's duct courses anteriorly between the mylohyoid and hyoglossus, opening at the sublingual caruncle. Key anatomic relationships during excision include the marginal mandibular branch of the facial nerve (superficial to the gland, at risk during incision and dissection), the lingual nerve (which crosses Wharton's duct twice and is at risk during duct dissection), the hypoglossal nerve (CN XII, deep to the gland on the hyoglossus muscle), and the facial artery and vein (which pass through or adjacent to the gland).

### Sublingual Gland

The sublingual gland is the smallest major gland and produces predominantly mucous secretion. It is located in the floor of mouth between the mucosa and mylohyoid muscle. Multiple small ducts (ducts of Rivinus) open along the sublingual fold. Bartholin's duct may join Wharton's duct or open independently. The sublingual gland is associated with ranula formation (mucous extravasation cyst).

![Anatomic illustration showing the three major salivary glands with their ductal systems and critical neurovascular relationships](images/salivary-gland-anatomy.jpg)

## Salivary Gland Pathology

### Inflammatory and Obstructive Disease

Sialolithiasis involves calcified stones in ducts or glandular parenchyma, with the submandibular gland accounting for 80 to 90% of cases because Wharton's duct is longer, wider, and courses against gravity. Sialadenitis is acute or chronic glandular infection, often secondary to obstruction, dehydration, or ductal stricture. Parotitis may be viral (mumps, now rare) or bacterial (Staphylococcus aureus is most common in acute suppurative parotitis). Chronic sclerosing sialadenitis (Kuttner tumor) is an IgG4-related disease of the submandibular gland that mimics neoplasm.

### Cystic Lesions

Mucoceles are mucous extravasation cysts, most common in the minor salivary glands of the lower lip. Ranulas are mucous extravasation cysts of the sublingual gland and may be simple (intraoral) or plunging (extending below the mylohyoid). Lymphoepithelial cysts occur in the parotid and are associated with HIV infection. First branchial cleft cysts may present as parotid masses and have an intimate relationship with the facial nerve.

### Autoimmune Disease

Sjogren syndrome is a chronic autoimmune destruction of the salivary and lacrimal glands, causing dry mouth (xerostomia) and dry eyes (keratoconjunctivitis sicca). Diagnosis involves anti-SSA/Ro and anti-SSB/La antibodies and minor salivary gland biopsy (focus score of 1 or greater). There is a 44-fold increased risk of MALT lymphoma.

### Neoplasms

#### Benign Tumors (65-80% of salivary neoplasms)

Pleomorphic adenoma is the most common salivary gland tumor (60-70%), a mixed tumor with epithelial and mesenchymal components that carries a risk of malignant transformation if left untreated (carcinoma ex pleomorphic adenoma). Warthin tumor (papillary cystadenoma lymphomatosum) is the second most common benign tumor, occurring almost exclusively in the parotid, bilateral in 10% of cases, and associated with smoking. Oncocytoma is rare and composed of oncocytes (mitochondria-rich cells).

#### Malignant Tumors

Mucoepidermoid carcinoma is the most common malignant salivary gland tumor, graded as low, intermediate, or high, with prognosis varying by grade. Adenoid cystic carcinoma is notorious for perineural invasion and late distant metastases (lung), following a slow but relentless course. Acinic cell carcinoma is low-grade and predominantly involves the parotid. Salivary duct carcinoma is high-grade and aggressive, resembling breast ductal carcinoma with common HER2 amplification. Carcinoma ex pleomorphic adenoma arises from longstanding or recurrent pleomorphic adenoma.

### Rule of Thumb for Salivary Neoplasms

The smaller the gland, the higher the percentage of tumors that are malignant. In the parotid, 20 to 25% of tumors are malignant. In the submandibular gland, 40 to 50% are malignant. In the sublingual and minor salivary glands, 50 to 80% are malignant.

![Table comparing the frequency of benign and malignant tumors by salivary gland location](images/salivary-tumor-frequency.jpg)

## Diagnostic Workup

### Imaging

Ultrasound is the first-line imaging modality for palpable masses, identifying solid versus cystic lesions and guiding FNA. CT with contrast evaluates the extent of tumor, lymph node involvement, and bone invasion. MRI provides superior soft tissue detail and evaluates perineural spread and deep lobe parotid tumors. Sialography is a contrast study of the ductal system useful for strictures and sialolithiasis, though it has been largely replaced by MR sialography. CBCT identifies radiopaque sialoliths in the dentoalveolar region.

### Fine-Needle Aspiration (FNA)

FNA is the first-line diagnostic tool for salivary gland masses, with sensitivity of 85 to 95% for distinguishing benign from malignant. Core needle biopsy is used when FNA is non-diagnostic. Incisional biopsy is generally contraindicated for parotid masses due to risk of facial nerve injury, tumor seeding, and fistula.

### Laboratory Studies

An autoimmune workup is performed if Sjogren syndrome is suspected (ANA, SSA, SSB, RF). Serum amylase may be elevated in acute parotitis. IgG4 levels are checked for IgG4-related disease.

![Ultrasound and MRI images demonstrating a pleomorphic adenoma of the superficial lobe of the parotid gland](images/parotid-tumor-imaging.jpg)

## Clinical Pearls

The facial nerve divides the parotid into superficial and deep lobes, and knowledge of its course is paramount for safe parotid surgery. The submandibular gland accounts for 80 to 90% of sialolithiasis due to the anatomy of Wharton's duct. The smaller the salivary gland, the greater the proportion of malignant tumors. FNA is the standard initial diagnostic step for salivary masses, and incisional biopsy of parotid tumors should be avoided. Adenoid cystic carcinoma has a predilection for perineural invasion and late pulmonary metastases, requiring long-term follow-up.

## References

1. Carlson ER, Schlieve T. "Salivary Gland Surgery." In: Miloro M, et al., eds. *Peterson's Principles of Oral and Maxillofacial Surgery*. 4th ed. Springer; 2022.
2. Witt RL. *Salivary Gland Diseases: Surgical and Medical Management*. 2nd ed. Thieme; 2016.
3. Speight PM, Barrett AW. "Salivary Gland Tumours: Diagnostic Challenges and an Update on the Latest WHO Classification." *Diagnostic Histopathology*. 2020;26(4):147-158.
4. Kessler AT, Bhatt AA. "Review of the Major and Minor Salivary Glands, Part 1: Anatomy, Infectious, and Inflammatory Processes." *Journal of Clinical Imaging Science*. 2018;8:47.