27 September 2026 · 0 views

Pleomorphic Adenoma of Lower Lip: Case Report

A Case Report of Pleomorphic Adenoma of the Lower Lip: An Uncommon Location and a Diagnostic Pitfall

1. Introduction

1.1 Overview of Minor Salivary Gland Tumors (MSGTs)

Minor salivary gland tumors (MSGTs) account for 10% to 15% of all salivary gland neoplasms. Unlike major salivary gland tumors, which are predominantly benign and localize mainly to the parotid gland, MSGTs demonstrate an equal or higher rate of malignancy, ranging between 40% and 50% depending on the anatomical subsite.

The oral cavity contains between 450 and 1,000 minor salivary glands distributed throughout the submucosa. The hard and soft palates represent the primary anatomical site for MSGTs, hosting roughly 50% of all reported cases. The buccal mucosa, retromolar trigone, floor of the mouth, and labial mucosa account for the remainder. Pleomorphic adenoma (PA), or benign mixed tumor, is the most common benign neoplasm among MSGTs. It features a diverse histology characterized by a mixture of ductal epithelial, myoepithelial, and mesenchymal-like stromal components.

1.2 The Lower Lip as an Atypical Site

The labial mucosa is an uncommon site for salivary gland neoplasms, accounting for less than 5% of all MSGTs. An anatomical divergence exists between the upper and lower lips:

Upper Lip: Sites predominantly host canalicular adenomas and pleomorphic adenomas. Approximately 75% to 80% of labial MSGTs arise in the upper lip, with most benign lesions presenting as encapsulated nodules.
Lower Lip: Lower lip MSGTs are rare, representing under 20% of all labial tumors. Over 50% to 60% of lower lip MSGTs are malignant, with mucoepidermoid carcinoma and adenoid cystic carcinoma presenting most frequently.

+----------------------------------------------------------------------+
|                    Labial MSGT Site Distribution                     |
+------------------------------------+---------------------------------+
| Upper Lip (~80% of Cases)          | Lower Lip (~20% of Cases)       |
+------------------------------------+---------------------------------+
| Predominantly Benign               | High Malignancy Rate (~50-60%)  |
| Most Common: Canalicular Adenoma,  | Most Common: Mucoepidermoid Ca, |
| Pleomorphic Adenoma                | Adenoid Cystic Ca, Rare PA      |
+------------------------------------+---------------------------------+

Because benign neoplasms rarely arise in the lower lip, solitary nodules are often misdiagnosed as reactive or non-neoplastic entities, such as mucoceles or irritation fibromas. Identifying a firm lower lip mass as a benign pleomorphic adenoma requires histopathological confirmation to avoid inadequate excision or overtreatment.

2. Case Presentation

2.1 Patient History and Clinical Findings

A 48-year-old female presented with a persistent, painless swelling on the inner aspect of the left lower lip. The lesion had been present for approximately 18 months, with gradual enlargement over the preceding six months. The patient reported no history of local trauma, biting habits, numbness, or discharge. Past medical and surgical histories were non-contributory.

+---------------------+------------------------------------------------+
| Clinical Parameter  | Finding                                        |
+---------------------+------------------------------------------------+
| Patient Age / Sex   | 48 years / Female                              |
| Location            | Left lower labial mucosa, submucosal           |
| Duration            | 18 months (slow progression)                   |
| Dimensions          | 1.5 cm x 1.2 cm x 1.0 cm                       |
| Palpation           | Firm, well-circumscribed, mobile, nontender   |
| Mucosal Appearance  | Normal color, non-ulcerated, intact vascularity|
| Regional Nodes      | No cervical lymphadenopathy                    |
+---------------------+------------------------------------------------+

Extraoral examination showed a mild, non-distorting asymmetry of the lower lip vermilion. Intraoral examination revealed a solitary, well-circumscribed, submucosal nodule measuring 1.5 cm x 1.2 cm in the left lower labial mucosa, lateral to the midline.

The overlying mucosa was intact, smooth, pink, and free of ulceration, telangiectasia, or secondary inflammation. Palpation revealed a firm, mobile, non-tender mass with distinct margins that did not adhere to the underlying mandible. Mental nerve sensory distribution was intact. Bilateral palpation of the submental, submandibular, and deep cervical lymph node chains demonstrated no lymphadenopathy.

2.2 Preoperative Diagnostic Considerations

Given its slow growth, circumscribed margins, and mucosal preservation, the lesion presented several differential diagnoses:

Extravasation Mucocele: The most common benign labial mass; typically fluctuant, bluish, and linked to ductal trauma. The firm consistency and prolonged 18-month duration made a classic mucocele less probable.
Irritation Fibroma: A common reactive lesion resulting from chronic microtrauma. It presents as a firm, pale nodule, though it is usually smaller and superficial.
Mesenchymal Neoplasms (Lipoma, Schwannoma, Neurofibroma): Submucosal, well-delineated lesions with varying consistency on palpation.
Malignant Minor Salivary Gland Tumors: Mucoepidermoid carcinoma and adenoid cystic carcinoma must remain high on the differential for any lower lip salivary mass due to site-specific malignancy rates.

+--------------------------------------------------------------------------+
|                     Lower Lip Nodule Differential                        |
+--------------------------+-----------------------+-----------------------+
| Diagnosis                | Consistency           | Diagnostic Pitfall    |
+--------------------------+-----------------------+-----------------------+
| Extravasation Mucocele   | Fluctuant / Soft      | Overdiagnosis based   |
|                          |                       | on site frequency     |
| Irritation Fibroma       | Firm / Fibrotic       | Mistaken for reactive |
|                          |                       | connective tissue     |
| Pleomorphic Adenoma      | Firm / Rubbery / Lobed| Underdiagnosed due to |
|                          |                       | lower lip rarity      |
| Mucoepidermoid Carcinoma | Firm / Variable       | Low-grade tumors mimic|
|                          |                       | benign lesions        |
+--------------------------+-----------------------+-----------------------+

The clinical presentation mimicked a benign connective tissue lesion, masking its salivary gland origin.

3. Diagnostic Modalities and Imaging

3.1 Preoperative Investigations

High-Resolution Ultrasonography (HR-US) using a 12–15 MHz linear transducer serves as a useful non-invasive imaging modality for superficial labial masses. Ultrasonographic assessment of this lesion revealed:

A well-defined, oval, hypoechoic nodule measuring 14.8 mm in maximal diameter.
Posterior acoustic enhancement with clean, regular borders.
Minimal internal vascularity on Color Doppler, ruling out high-flow vascular malformations.

+------------------------------------------------------------------------+
|                      HR-US Diagnostic Profile                          |
+--------------------+---------------------------------------------------+
| Feature            | Ultrasound Observation                            |
+--------------------+---------------------------------------------------+
| Margins            | Well-demarcated, thin echogenic boundary capsule  |
| Echogenicity       | Homogeneously hypoechoic                          |
| Acoustic Shadowing | Posterior acoustic enhancement present            |
| Vascularity        | Low-resistance, sparse peripheral/central flow     |
+--------------------+---------------------------------------------------+

Fine-Needle Aspiration Cytology (FNAC) provides high accuracy in parotid lesions (sensitivity >85–90%), but its utility in small, mobile labial nodules remains limited. The fibrous or chondromyxoid matrix can lead to dry taps, low cellularity, or non-representative sampling. Core needle biopsy is rarely indicated for small, accessible lip masses due to risks of capsular rupture and tumor seeding. An excisional biopsy was selected for this patient.

3.2 Navigating Diagnostic Pitfalls

Cytological and limited incisional biopsies of labial MSGTs involve distinct diagnostic traps:

Hypocellular Samples: Predominantly myxoid stroma with sparse epithelial elements can be misidentified as normal salivary retention phenomena or benign mesenchymal tissue.
Cellular Atypia vs. Metaplasia: Metaplastic squamous changes within ductal segments of a pleomorphic adenoma can be misclassified as squamous cell carcinoma or mucoepidermoid carcinoma.
Myoepithelial Predominance: Monomorphic populations of myoepithelial cells mimic myoepithelioma, cellular pleomorphic adenoma, or adenoid cystic carcinoma (cribriform variants).

Biopsy breaches the fibrous pseudocapsule. If an unencapsulated incision is performed without clear margins, neoplastic myoepithelial cells may seed the surrounding orbicularis oris muscle fibers, increasing the risk of recurrence.

4. Surgical Management

4.1 Surgical Technique and Approach

Excision was performed under local infiltration anesthesia (2% lidocaine with 1:100,000 epinephrine). A linear, horizontal incision was placed along the labial mucosa parallel to the relaxed skin tension lines and mucosal folds, directly over the prominence of the mass.

+------------------------------------------------------------------------+
|                     Surgical Protocol Steps                            |
+------+-----------------------------------------------------------------+
| Step | Operative Detail                                                |
+------+-----------------------------------------------------------------+
| 1    | Transmucosal incision parallel to orbicularis oris fibers.     |
| 2    | Blunt, micro-dissection around the fibrous pseudocapsule.      |
| 3    | Inclusion of an intact margin of normal surrounding minor      |
|      | salivary lobules to prevent micro-capsular dehiscence.          |
| 4    | Identification and preservation of mental nerve branches.       |
| 5    | Muscle re-approximation using 4-0 absorbable polyglactin sutures.|
| 6    | Interrupted mucosal closure with 5-0 fast-absorbing sutures.   |
+------+-----------------------------------------------------------------+

Submucosal blunt dissection preserved the integrity of the fibrous capsule. The dissection isolated the mass from the underlying orbicularis oris muscle without transecting muscle bundles. Adjacent normal minor salivary gland lobules were included at the peripheral margins to avoid unroofing micro-protrusions or satellite nodules. Mental nerve sensory branches running along the inferior labial plane were identified and protected.

[ Mucosal Surface ]
   │
   ├─ Horizontal Incision (Parallel to fibers)
   │
   ├─ Blunt Dissection (Extra-capsular boundary)
   │     ├─ [ Intact Fibrous Pseudocapsule ]
   │     │     └─ [ Epithelial & Myoepithelial Tumor Mass ]
   │     └─ [ Adjacent Minor Salivary Lobules Rim ]
   │
[ Orbicularis Oris Muscle Layer ] ──> Preserved / Re-approximated

4.2 Intraoperative and Postoperative Considerations

Hemostasis was maintained using bipolar electrocautery to prevent hematoma formation, which can induce labial fibrosis and vermilion distortion. The surgical field was irrigated with sterile saline, and the muscular layer was closed using interrupted 4-0 polyglactin sutures. Mucosal edges were realigned and closed with interrupted 5-0 fast-absorbing polyglactin sutures.

Postoperative recovery was uneventful. The patient was managed with short-term non-steroidal anti-inflammatory drugs (NSAIDs) and chlorhexidine gluconate (0.12%) oral rinses. Complete mucosal re-epithelialization occurred within 14 days without paresthesia, motor deficit, or contour abnormalities of the lower lip.

5. Histopathological and Immunohistochemical Evaluation

5.1 Microscopic Architecture

Gross examination revealed a firm, well-circumscribed, grayish-white, lobulated tissue mass measuring 1.5 cm x 1.2 cm x 1.0 cm. The cut surface was solid, glistening, and homogeneous, without cystic degeneration, hemorrhage, or necrotic foci.

+-----------------------------------------------------------------------+
|                    Histomorphological Features                        |
+--------------------+--------------------------------------------------+
| Component          | Microscopic Findings                             |
+--------------------+--------------------------------------------------+
| Epithelial         | Ducts, tubules, and cords lined by cuboidal cells|
|                    | containing eosinophilic material                 |
| Myoepithelial      | Polygonal, spindle-shaped, and plasmacytoid cells|
|                    | blending into the surrounding matrix             |
| Stromal Matrix     | Mixed chondromyxoid, myxoid, and hyalinized zones |
| Pseudocapsule      | Continuous, thin fibrous rim without capsular    |
|                    | perforation or perineural invasion               |
+--------------------+--------------------------------------------------+

Microscopic evaluation with Hematoxylin and Eosin (H&E) staining confirmed a classic biphasic pleomorphic adenoma. The tumor consisted of:

Ductal Epithelial Cells: Arranged in distinct ductules, small cysts, and anastomosing trabeculae filled with periodic acid–Schiff (PAS)-positive eosinophilic coagulum.
Myoepithelial Cells: Variable morphology showing spindle, angular, and plasmacytoid (hyaline) variants transitioning directly into the stroma.
Mesenchymal/Stromal Elements: Abundant chondromyxoid, myxoid, and hyalinized collagenous matrix interspersed between cellular islands.

The lesion was bounded by a thin, intact fibrous pseudocapsule. No capsular penetration, nuclear pleomorphism, atypical mitotic figures, or perineural or lymphovascular invasions were detected.

5.2 Immunohistochemistry (IHC) Profile

Immunohistochemical staining confirmed the biphasic differentiation of the tumor components:

+----------------------------------------------------------------------+
|                     IHC Marker Specificity Profile                   |
+---------------+------------------------+-----------------------------+
| Marker        | Target Cell Population | Reaction Intensity          |
+---------------+------------------------+-----------------------------+
| CK7 / Pan-CK  | Ductal Luminal Cells   | Strongly Positive (Diffuse) |
| S100 Protein  | Myoepithelial Cells    | Strongly Positive (Diffuse) |
| SMA           | Myoepithelial Cells    | Positive (Periductal)       |
| p63           | Basal / Myoepithelial  | Strongly Positive (Nuclear) |
| Calponin      | Contractile Elements   | Positive                    |
| Ki-67         | Proliferation Index    | < 2% (Low Growth Fraction)  |
+---------------+------------------------+-----------------------------+

Cytokeratin 7 (CK7) & AE1/AE3: Positive in luminal epithelial cells defining the inner layer of ductal structures.
S100 Protein: Strong, diffuse cytoplasmic and nuclear positivity across modified myoepithelial and chondroid cells.
Smooth Muscle Actin (SMA) & Calponin: Positive in the abluminal, contractile myoepithelial cells.
p63: Strong nuclear expression in basal and non-luminal cellular layers.
Ki-67: Low proliferation index (<2%), confirming the benign nature of the lesion and excluding Carcinoma ex Pleomorphic Adenoma (CXPA).

6. Discussion and Literature Review

6.1 Clinical Behavior and Recurrence Mechanisms

Pleomorphic adenomas of the lower lip present unique clinical hurdles compared to their major salivary gland and palatal counterparts. Lower lip PA cases represent under 2% to 5% of all benign MSGTs. Because clinicians encounter non-neoplastic retention phenomena (mucoceles) and benign connective tissue lesions with greater frequency in this region, lower lip pleomorphic adenomas are rarely listed as the initial provisional diagnosis.

+-----------------------------------------------------------------------+
|                    Pleomorphic Adenoma Recurrence Factors             |
+---------------------------+-------------------------------------------+
| Etiology                  | Pathological / Surgical Mechanism         |
+---------------------------+-------------------------------------------+
| Incomplete Enucleation    | Stripping tumor tissue leaves microscopic |
|                           | capsular projections behind               |
| Pseudopod Extensions      | Outgrowths beyond the main tumor body     |
| Intraoperative Rupture    | Tumor cell spillage into the surgical bed |
| Incomplete Margin Margins | Failure to remove bordering satellite     |
|                           | salivary tissue                           |
+---------------------------+-------------------------------------------+

Recurrence in pleomorphic adenoma is primarily driven by:

Intraoperative Tumor Spillage: Fragile myxoid stroma can tear during simple enucleation. Spilled chondromyxoid and epithelial elements can implant, leading to multinodular, metachronous recurrences throughout the surgical site.
Capsular Incompleteness and Pseudopods: MSGT pseudocapsules are often thin or pathologically incomplete. Simple “shelling-out” leaves microscopic extensions behind.
Malignant Transformation: While rare in MSGTs, untreated or multiply recurrent pleomorphic adenomas can transform into Carcinoma ex Pleomorphic Adenoma over 15 to 20 years. The transformation risk increases from 1.5% in tumors under five years duration to over 9.5% in those untreated for more than fifteen years.

6.2 Best Practices for Oral Surgeons and Pathologists

To mitigate the risks associated with this diagnostic pitfall, surgical and pathology teams should adhere to a structured protocol:

                  [ Firm, Isolated Lower Lip Mass ]
                                 │
                 ┌───────────────┴───────────────┐
         [ High Suspicion ]              [ Routine Firm Nodule ]
                 │                               │
         [ Pre-op HR-US ]                 [ High-Res US ]
                 │                               │
                 └───────────────┬───────────────┘
                                 │
                 [ Extracapsular Local Excision ]
           (Intact Pseudocapsule + 1-2 mm Normal Rim)
                                 │
            ┌────────────────────┴────────────────────┐
    [ Clear Margins & IHC ]                  [ Ruptured/Incomplete ]
            │                                         │
  [ Standard Review (1-3 yr) ]              [ Long-term Monitoring ]
                                               (5-10 yr Surveillance)

Preoperative Assessment: Treat any firm, solitary, non-fluctuant lower lip nodule lacking trauma history as a potential neoplasm rather than a standard mucocele. Use high-resolution ultrasound to verify margins and exclude deep muscular infiltration.
Surgical Technique: Avoid simple intracapsular enucleation. Perform an extracapsular local excision with a 1–2 mm buffer of surrounding minor salivary lobules and submucosa, keeping the pseudocapsule intact throughout resection.
Pathology Protocol: Perform step-serial sectioning through the specimen. Use dual-staining IHC (CK/p63/S100/Ki-67) to confirm biphasic cellularity and rule out malignant transformation or high-grade components.
Follow-Up Schedule: Monitor the patient annually for at least 5 years. Given the slow growth kinetics of recurrent pleomorphic adenoma, late recurrences can manifest 7 to 10 years after initial surgery.

7. Conclusion

Pleomorphic adenoma of the lower lip is an uncommon entity that represents a diagnostic pitfall for oral clinicians and pathologists. Its clinical similarity to mucoceles and irritation fibromas can lead to misdiagnosis, capsular violation, or incomplete excision.

Extracapsular surgical resection with a margin of healthy surrounding tissue provides definitive treatment while preserving oral function and aesthetics. Histopathological evaluation supported by an immunohistochemical panel (S100, CK7, p63, SMA) remains essential to confirm the diagnosis and verify clear margins.

8. Frequently Asked Questions (FAQ)

How common is pleomorphic adenoma in the lower lip?

Pleomorphic adenoma accounts for most benign salivary gland neoplasms, but lower lip occurrences make up less than 2% to 5% of all minor salivary gland pleomorphic adenomas. Most labial salivary tumors develop in the upper lip.

Why is pleomorphic adenoma of the lower lip considered a diagnostic pitfall?

Its slow, asymptomatic growth and circumscribed nature mimic common lower lip lesions such as extravasation mucoceles, irritation fibromas, or lipomas. Because benign MSGTs are rare in the lower lip—where malignancies occur more frequently—clinicians may underdiagnose the mass or choose suboptimal excision techniques.

What is the primary treatment for a labial pleomorphic adenoma?

Complete extracapsular surgical excision with an intact fibrous pseudocapsule and a 1–2 mm cuff of surrounding normal tissue is the definitive treatment. Simple enucleation (shelling out) increases the risk of capsular rupture, tumor spillage, and recurrence.

Can pleomorphic adenoma of the lip turn into cancer?

Yes. Malignant transformation into Carcinoma ex Pleomorphic Adenoma is rare in minor salivary glands, but the risk increases in long-standing, untreated, or multiply recurrent tumors.

What is the expected recurrence rate after excision?

The recurrence rate is low (under 5%) when the lesion is completely excised with intact margins. Recurrences are typically caused by intraoperative capsular rupture, incomplete resection of pseudopods, or tumor cell spillage into the wound bed.

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