Rare Tumor Hiding Inside a Salivary Gland Lymph Node Challenges Pathologists

A firm lump in front of the ear is one of the most alarming findings a patient can bring to a doctor, because the parotid salivary gland sits directly over a network of lymph nodes that drain the face and scalp, and masses in this region frequently turn out to be metastatic cancer. When a 30-year-old patient presented with a slowly enlarging, tender mass in the right parotid region, clinicians faced exactly this diagnostic dilemma. What surgeons removed and pathologists examined, however, proved to be something almost no one has seen before: a benign nerve sheath tumor growing entirely within a lymph node inside the salivary gland, and apparently only the second such case ever reported with predominantly epithelioid morphology.

The case, reported by researchers at Shahid Sadoughi University of Medical Sciences in Yazd, Iran, in the journal Case Reports in Pathology, describes a well-circumscribed mass measuring approximately 27 by 19 millimeters in the superficial lobe of the right parotid gland. Preoperative imaging with contrast-enhanced computed tomography showed a homogeneous, mildly enhancing lesion without invasion of surrounding structures, and fine-needle aspiration cytology was initially interpreted as suspicious for a low-grade neoplasm. Because the mass was located in the superficial parotid lobe and the facial nerve runs through the gland, the surgical team performed a superficial parotidectomy with careful dissection and preservation of the facial nerve branches. The postoperative course was uneventful, and the patient retained normal facial nerve function.

Gross examination of the surgical specimen revealed a firm, gray-white, well-demarcated tumor measuring 27 by 19 by 15 millimeters, and the defining surprise came when the pathologists identified the tumor sitting entirely within an intraparotid lymph node. Microscopic evaluation showed a neoplasm composed of spindle and epithelioid cells arranged in intersecting fascicles, with focal nuclear palisading reminiscent of Verocay bodies, the characteristic structures of schwannoma. The tumor was completely encapsulated by a thin fibrous capsule and surrounded by a rim of compressed residual lymphoid tissue, confirming its origin within the lymph node rather than the salivary gland parenchyma. There was no evidence of necrosis, increased mitotic activity, or extension beyond the lymph node capsule.

Immunohistochemical staining was essential to establishing the diagnosis. The tumor cells showed diffuse, strong positivity for S-100 protein, the hallmark neural marker, and were also positive for SOX10, another neural crest transcription factor. Staining for cytokeratins, smooth muscle actin, desmin, CD34, and melanocytic markers including HMB-45 and Melan-A was negative. The proliferation index measured by Ki-67 staining was low, at approximately 3 percent. This staining profile excluded metastatic carcinoma, melanoma, myoepithelial tumors, and solitary fibrous tumor, leaving benign schwannoma as the only diagnosis consistent with both the morphology and the immunophenotype.

The epithelioid variant of schwannoma is itself uncommon, accounting for a small minority of all schwannomas, and is characterized by sheets and nests of polygonal epithelioid cells rather than the classic spindle cell pattern. Epithelioid morphology raises particular concern for epithelioid malignant peripheral nerve sheath tumor, melanoma, and metastatic carcinoma, all of which can show overlapping cytological features. In this case, the complete encapsulation, absence of necrosis and significant atypia, low Ki-67 index, and strong diffuse S-100 and SOX10 positivity argued decisively against malignancy. The researchers emphasized that epithelioid schwannoma should be included in the differential diagnosis of epithelioid neoplasms of the head and neck, even in unusual locations such as lymph nodes.

Intranodal schwannoma is extraordinarily rare, with only a handful of cases reported in the literature, most arising in cervical lymph nodes of the neck. To the authors’ knowledge, only one previous case of schwannoma arising within an intraparotid lymph node has been documented, reported in 2009, and that tumor showed classic spindle cell morphology rather than the epithelioid pattern seen here. The researchers conducted a comprehensive review of the literature and found no previous report of an epithelioid schwannoma arising within an intraparotid lymph node, making this apparently the first such case ever described.

The researchers highlighted the diagnostic challenges posed by this unusual presentation. A mass within a parotid lymph node is most commonly metastatic carcinoma or melanoma draining from the skin of the face, scalp, or external ear, and this clinical context dominates preoperative decision-making. Fine-needle aspiration cytology in this case was reported as suspicious for a low-grade neoplasm but could not establish the specific diagnosis, and the researchers noted that cytological evaluation of schwannoma is frequently difficult because of the tumor’s low cellularity and the frequent absence of the characteristic Antoni A and Antoni B patterns in aspirated material. Definitive diagnosis therefore required complete surgical excision and histopathological examination.

The researchers also discussed the importance of distinguishing benign epithelioid schwannoma from epithelioid malignant peripheral nerve sheath tumor, a rare and aggressive malignancy. Epithelioid malignant peripheral nerve sheath tumor typically shows marked cytological atypia, necrosis, high mitotic activity, and loss of H3K27me3 expression, features entirely absent in this case. The researchers noted that INI1 expression was retained in the tumor cells, providing additional support for the benign diagnosis, although they acknowledged that the distinction between benign and malignant epithelioid nerve sheath tumors can occasionally be difficult and requires careful correlation of morphology, immunophenotype, and clinical behavior.

The prognosis for benign schwannoma is excellent, and complete surgical excision is curative. The researchers reported that the patient remained well without evidence of recurrence at follow-up. They recommended long-term clinical and imaging follow-up given the extraordinary rarity of intranodal schwannoma and the limited literature available on its natural history. The researchers concluded that this case expands the recognized spectrum of schwannoma presentations and underscores the importance of considering benign nerve sheath tumors in the differential diagnosis of epithelioid neoplasms of the head and neck, even when they arise in locations where malignancy is overwhelmingly more likely.

Subject of Research: Pathology

Article Title: Intranodal Epithelioid Schwannoma in an Intraparotid Lymph Node: A Case Report and Literature Review

Article References: Vajihinejad, M., Najafi, K., Ahrar, M. H., & Shamsi, A. (2026). Intranodal Epithelioid Schwannoma in an Intraparotid Lymph Node: A Case Report and Literature Review. Clinical Case Reports, 14(10), Article e73709. https://doi.org/10.1002/ccr3.73709

Image Credits: AI Generated

DOI: 10.1002/ccr3.73709

Keywords: schwannoma, pathology, parotid gland, lymph node, nerve sheath tumor, differential diagnosis, immunohistochemistry, case report, Intranodal, Epithelioid, Intraparotid, Lymph