Primary mucoepidermoid carcinoma of scalp: a case report

Abstract

Background

Mucoepidermoid carcinoma of the skin is an exceedingly rare neoplasm, with only a limited number of cases documented in the literature. Typically, mucoepidermoid carcinoma arises in the salivary glands, where it accounts for 30% of all malignant salivary gland tumors and generally presents as a low-grade malignancy with a low probability of metastasis.

Case presentation

We report a case of a 49-year-old female patient of African origin who presented to our tertiary center with a longstanding scalp lesion that had been present for approximately 10 years. Initially, the lesion was roughly the size of a tennis ball and remained stable until about 3 months prior to presentation, when it was excised at a peripheral primary health center. Unfortunately, no histological analysis or follow-up was conducted after the excision, and the lesion recurred, progressively increasing in size. The patient reported no cardinal B-symptoms or central nervous system symptoms at any point. Histopathological analysis of the recurrent mass confirmed a diagnosis of mucoepidermoid carcinoma, and a complete surgical excision was subsequently performed. Following surgery, the patient was referred to the national oncology center for radiotherapy as part of her comprehensive oncological management. She is currently 8 months post-excision, receiving radiotherapy, and exhibits no clinical signs of recurrence.

Conclusion

Mucoepidermoid carcinoma originating in cutaneous sites is particularly unusual and may stem from the embryonic development of ectopic salivary glands within the skin. In this case report, we describe a unique presentation of primary mucoepidermoid carcinoma on the scalp, which demonstrated aggressive characteristics with suspected metastasis to the vertebral body. This case highlights the importance of considering mucoepidermoid carcinoma in the differential diagnosis of scalp masses and underscores the need for further investigation into its pathogenesis and metastatic potential.

Background

Mucoepidermoid carcinoma (MEC) is among the most frequently diagnosed malignancies of the salivary glands, alongside adenoid cystic carcinoma (ACC) and acinic cell carcinoma (AciCC) [1]. MEC is characterized histologically by a mix of three distinct cell types: epidermoid, mucus-secreting, and intermediate cells, which together contribute to its unique pathology [2, 3]. While it commonly originates in the salivary glands, MEC rarely manifests in cutaneous locations. Primary cutaneous MEC is particularly uncommon and is thought to arise from ectopic salivary gland tissue embedded within the skin.

In this case report, we describe a highly unusual presentation of primary MEC on the scalp, which persisted for more than a decade before presenting with notable clinical changes, emphasizing the importance of awareness and timely diagnosis of this rare cutaneous malignancy.

Case presentation

We present a 49-year-old female patient of African origin who attended our outpatient neurosurgical clinic with a longstanding history of a scalp mass. The mass had been present for more than 10 years, initially appearing as a small lump slightly smaller than a tennis ball. The lesion remained non-progressive and nontender until approximately 5 months prior, when it was excised at a peripheral primary healthcare facility; unfortunately, the tissue was not sent for histopathological examination. In the 5 months following excision, the lesion recurred, gradually increased in size, and developed ulceration, with a tendency to bleed easily upon contact. Concerned by these developments, the patient sought medical attention at our tertiary center. She denied any history of convulsions, headache, loss of consciousness, or weakness.

On clinical evaluation, the patient was alert, fully conscious, and exhibited no signs of pallor or jaundice. There was no peripheral lymphadenopathy, and her vital signs were within the normal range. Local examination of the scalp revealed two distinct masses on the right side. The larger mass was fungating, approximately 9 × 7 cm in size, tender, prone to bleeding, and mildly mobile. The second lesion, measuring approximately 3 × 3 cm, was non-fungating (Fig. 1A).

Fig. 1

A Clinical photograph showing fungating scalp mass, B postoperative photograph after wide local excision of scalp lesion, C photo of excised scalp lesion (was submitted whole for histopathology analysis)

The patient’s laboratory and imaging studies provided a detailed picture of her condition. Her complete blood count (CBC) was within normal limits, showing a leukocyte count of 9.43 × 10⁹/L, normochromic normocytic red blood cells with a hemoglobin level of 13.8 g/dL, and a normal platelet count of 293 × 10⁹/L. Her serum creatinine was 55 µmol/L, with electrolyte levels showing a sodium of 133 mmol/L and potassium of 5.5 mmol/L, all within acceptable ranges. Imaging studies included a normal chest X-ray, along with abdominal and pelvic ultrasound findings that were also unremarkable. A head and neck computed tomography (CT) scan revealed a multilobulated hyperdense ulcerative scalp lesion located on the right frontal region of the scalp, measuring 9 × 7.8 × 6 cm. Notably, there was no skull bone erosion, and no intracranial extension of the mass was observed. Enlarged bilateral cervical lymph nodes were seen at levels I and II. Additionally, magnetic resonance imaging (MRI) of the spine showed a pathological compression fracture of the T10 vertebral body with no stenosis of the canal, raising a high suspicion for vertebral metastasis (Fig. 2). She was deemed clinical advanced stage disease (IVc) according to the American Joint Committee on Cancer (AJCC), with local–regional and distant metastasis.

Fig. 2

Post-contrast computed tomography scan images: A sagittal and B coronal planes showing a lobulated ulcerative heterogeneous enhancing soft tissue mass (yellow) involving the right superior parietal scalp; no underlying bone involvement nor intracranial extension; ipsilateral level I and II cervical lymphadenopathy also present (not shown in the images); C sagittal planes of T1W, T2-W, and fat sat sequences showing a T10 vertebral pathological compression fracture (red) and a T8 vertebral body fat sat hyperintense lesion in keeping with vertebral body metastasis

The biopsy of the lesion confirmed a diagnosis of mucoepidermoid carcinoma. Following this, the patient was counseled and consented for surgical management. The lesion was excised under general anesthesia with a wide local excision approach to ensure complete removal (Fig. 1B, C) and the defect was dressed by sterile medicated paraffin gauze. The excised tissue was sent for histopathological examination, which corroborated the initial biopsy finding of invasive mucoepidermoid carcinoma (Fig. 3). Post-surgery, the patient was referred to the Ocean Road Cancer Institute for further evaluation with positron emission tomography (PET) scan and consideration of radiotherapy. At 8-month follow-up post-excision, the patient shows no clinical signs of recurrence and has no central nervous system symptoms. The pathological vertebral fracture remained stable with no surgical intervention and the scalp wound is being followed up by plastic surgeons. This positive outcome underscores the successful initial surgical intervention and postoperative care.

Fig. 3

Photomicrograph of hematoxylin and eosin staining showing a solid tumor in a trabecular pattern with epidermoid cells (green arrow) surrounded by mucin pools (blue arrow) and foci of necrosis (yellow arrow)

Discussion and conclusion

Mucoepidermoid carcinoma (MEC) is a well-documented neoplasm accounting for approximately 30% of all malignant salivary gland tumors. However, cutaneous involvement is sporadic [4]. MEC was first established in 1945 by Stewart et al. as being characterized by a mixture of epidermoid and mucus-secreting cells [5, 6]. The first reported case of primary cutaneous MEC was by Gallager et al. in 1959, and since then, the medical literature has described a total of only 20 cases where cutaneous involvement was identified as the primary cause [4, 7, 8].

The etiopathogenesis of primary cutaneous MEC is unclear. Salivary glands have been suggested to derive from sweat glands due to their similarities in embryonic germ layer origin, histological structures, and functions. It has also been supported by several authors that the embryonic precursor of both salivary glands and sweat glands are analogous to the cutaneous mucin-secreting glands of amphibians. It is thus postulated that primary cutaneous MEC may have developed from an ectopic salivary gland derived from a sweat gland [9].

It typically presents as a flesh-colored nodule that ulcerates, most commonly occurring in the head and neck with slight male predominance [3]. Other sites include the axilla, vulvae, dorsal foot, and thighs [9]. Histologic classification most often divides cMEC into low-grade (well differentiated) and high-grade (poorly differentiated) subtypes, although an intermediate grade has also been proposed. In addition, three groups have been described on the basis of the proportion of mucin-secreting, squamous, intermediate, and clear cells and the degree of maturation of these cells [10]. By immunohistochemistry, the tumor cells express cytokeratin AE1/AE3, EMA, CEA, CK5/6, CK7, CK19, and p63 [11].

The typical differential diagnosis for this malignancy mostly encompasses squamous cell carcinoma, adenocarcinoma, undifferentiated carcinoma, melanoma, and lymphoma [8]. Overall, cMECs have a 5-year overall survival and disease-specific survival of 68.2% and 76%, respectively [11]. Treatment of MEC consists of surgery with adjuvant radiation therapy, as in our case, for intermediate and high-grade tumors. Tumor recurrence has been reported to be as high as 50% in high-grade lesions and 12.5% in low-grade MEC. Metastases from primary cutaneous MEC have been reported in up to 50% of cases [4]. The roles of both primary and adjuvant radiotherapy with or without chemotherapy are uncertain. From the limited cases, survival from 2 months to 2 years has been reported in cases treated with adjuvant radiotherapy [9].

Primary cutaneous mucoepidermoid carcinoma (MEC) is exceptionally rare, with only a limited number of cases documented in the literature. This tumor comprises a mix of mucus-secreting and epidermoid cells, distinguishing it histologically. MEC most commonly originates in the parotid glands, making its cutaneous presentation unusual. Clinical and radiological evaluations alone are often inconclusive for diagnosis, underscoring the importance of histopathological analysis for definitive identification. Given its unique presentation and rarity, treatment should be individualized to each case to ensure optimal outcomes.