Ancient schwannoma of the submandibular gland

Summary

Schwannomas, benign tumours derived from Schwann cells, exhibit slow growth rates and are commonly found extracranially in the head, neck and extremities. However, intraoral and salivary gland schwannomas are less frequent. Ancient schwannomas, characterised by histological degenerative changes, represent a rare variant.

This report pertains to a case study involving a man in his 40s who presented with a slow, progressive and painless mass in the right submandibular region persisting over 3 years.

CT revealed a well-defined multiloculated cystic mass in the right submandibular gland, later confirmed as an ancient schwannoma on excision and histological examination. Immediate postoperative complications included right marginal mandibular nerve palsy, fully resolving within 12 months. No recurrent tumours were detected in subsequent physical examinations and imaging.

Ancient schwannomas, although rare, can occur in the submandibular gland. Thorough multimodal diagnostic approaches are essential for accurate differentiation from other submandibular masses.

Background

Schwannomas are the most common peripheral nerve sheath tumours, originating from Schwann cells, a type of glial cell that surrounds neurons. They are well-encapsulated, slowly progressive and usually found as solitary masses. Schwannomas originate from both cranial nerves and peripheral nerves. Cranial nerve schwannoma commonly originates from sensory nerves, such as the vestibular nerve. Schwannomas of peripheral origin are commonly located in the flexural areas of the limbs, head and trunk.^{1 2} In rare instances, these tumours may originate from the salivary glands.³

Ancient schwannoma is an uncommon variant of schwannomas, which differs from its origin due to degenerative changes at the histological level. The histological findings of ancient schwannomas include calcification, cystic degeneration, haemorrhage and diffuse stromal hyalinisation.⁴ Ancient schwannomas of the submandibular gland are extremely rare, and few reports are available.

Case presentation

A male patient in his 40s, with no underlying health conditions, presented to our tertiary specialist unit with a right submandibular mass that had been present for 3 years. There was no history of treatment or intervention. The patient did not report any difficulties with eating or weight loss associated with the appearance of the mass. Physical examination revealed a painless, well-defined, mobile, smooth and firm mass measuring approximately 5.5×5.5 cm in the right submandibular region. No cervical lymphadenopathy or facial expression deficits were noted. The patient sought medical attention due to concern about the progressively enlarging mass.

Investigations

The patient underwent a fine-needle aspiration (FNA) biopsy and CT of the neck to evaluate the characteristics, size and position of the tumour for surgical assessment. The FNA results of the submandibular mass indicated granulomatous sialadenitis, and the official CT scan report described a well-circumscribed multiloculated cystic mass with enhancing mural solid component and several enhancing septa arising from the superolateral part of the right submandibular gland, measuring 3.4×3.4×4.4 cm, with multiple subcentimetre bilateral cervical lymph nodes (figure 1).

Figure 1. (A) Axial, (B) coronal (C) and sagittal view of CT of the neck with contrast media show a well-circumscribed multiloculated cystic mass on the right submandibular gland (arrow).

Treatment

Right submandibulectomy with cervical lymph node dissection groups I–IV was performed. Surgical resection of the right submandibular mass yielded a gross specimen consisting of a grey-brown tumour with attached fat tissue. The tumour itself measured 5.5×3.5×3.5 cm, whereas the soft tissue attached to it was 8×5×2 cm in size.

Outcome and follow-up

Histological examination revealed spindle cells with a biphasic pattern. Dense and loose areas were observed (figure 2). In dense regions, fascicles of spindle cells were noted, along with nuclear palisading and Verocay bodies (figure 3).

Figure 2. Spindle cell tumours are organised into dense regions (arrow) and loose regions (arrowhead), representing Antoni A and B patterns, respectively.

Figure 3. Fascicle of spindle cells with nuclear palisading and Verocay body in Antoni A region.

Nuclear atypia was occasionally noted. The loose area contained stellate-shaped cells, haemosiderin-laden macrophages and hyalinised blood vessels (figure 4). Mitotic figures were rarely encountered. Large cystic degeneration with foam cell infiltrates was presented (figure 5). All lymph nodes showed reactive lymph node hyperplasia with a prominent germinal centre. Conclusively, these results suggested a diagnosis of ancient schwannoma of the submandibular gland without evidence of malignancy in cervical lymph nodes.

Figure 4. Haemosiderin-laden macrophages and hyalinised blood vessels.

Figure 5. Cystic degeneration with foam cell infiltrates.

Anatomically, the submandibular gland is surrounded by three important nerves: the marginal mandibular nerve, the hypoglossal nerve and the lingual nerve. Hence, facial expression and tongue movement should be thoroughly evaluated preoperatively and postoperatively. Prior to the operation, the patient provided informed consent regarding the procedure and potential complications. Among the potential complications discussed with the patient beforehand is the occurrence of temporary or permanent marginal mandibular nerve palsy. In this case, the right marginal mandibular nerve could be identified and preserved following the dissection of the platysma. An immediate postoperative complication manifested as right marginal mandibular nerve palsy; the patient presented with dysfunction of the right depressor anguli oris muscle during the first few days, which persisted until 6 months after surgical resection. A postoperative CT scan at the 6-month follow-up revealed mild fascial thickening at the anterior right side of the neck, just anterolateral to the surgical bed, suggestive of postoperative changes. Nevertheless, there was no evidence of residual or recurrent tumours. The marginal mandibular nerve palsy had completely resolved at 12 months post-operation. Following an initial follow-up schedule of every 3 months during the first year, every 6 months in the second year and annual check-ups after that, the patient has shown no recurrence of the mass on physical examination over 7 years.

Discussion

Schwannomas are benign nerve sheath tumours that originate from the Schwann cells. These tumours can affect both sensory and motor nerves. Common locations for schwannomas include cranial nerves, with the eighth cranial nerve being the most frequently affected among the sensory nerves. Among the motor nerves, the facial nerve is the most common site. Peripheral nerve schwannomas are relatively uncommon. They can be found in nerves located in the head, trunk and flexural areas of the limbs. The most common sites for peripheral schwannomas are the flexural areas of the upper extremities.¹ Less frequently, peripheral schwannomas can be found in the salivary glands.^{2 3}

Schwannomas are typically asymptomatic, painless and exhibit slow progressive growth. However, symptomatic patients can present with pressure effects, resulting in pain, weakness, paresthesia and symptoms corresponding to the function of the affected nerves.¹

The diagnosis of schwannomas requires multimodal techniques, including imaging and histological analyses. Imaging modalities, primarily ultrasonography, suggest a well-demarcated, round, hypoechoic and homogeneous mass. Additionally, MRI is recommended because of its ability to visualise soft tissues. MRI findings typically show isointense or decreased signal intensity in T1-weighted images compared with skeletal musculature, whereas in T2-weighted images, they appear heterogeneously increased. Furthermore, the presence of a tumour adjacent to major nerves and positive radiological signs, such as fascicular, target and split fat signs, are suggestive of schwannomas.²

Histological findings of classical schwannomas consist of two major regions: highly dense cellular zones called Antoni A and less compact cellular zones called Antoni B. The compacted Antoni A zones are arranged in stacked conformations, consisting of bands of palisading nuclei alternating with acellular zones of cytoplasmic processes known as Verocay bodies. Antoni B areas are loosely arranged cellular zones containing spindle cells, abundant inflammatory cells and collagen fibres.⁴

There are several subtypes of schwannoma. These include classical, cellular, plexiform, melanotic, neuroblastoma-like, hybrid, pseudoglandular and ancient schwannomas.^{4 5} Ancient schwannoma, initially described by Ackerman and Taylor in 1951,⁶ is marked by its distinctive features such as degenerative nuclear atypia and various degenerative changes like cystic stromal alterations, haemorrhage, calcification and widespread stromal hyalinisation. The most notable feature of ancient schwannoma is its pronounced nuclear atypia, which can be misleading and may suggest malignancy. However, the discrepancy between the nuclear atypia and the absence of mitotic figures indicates that the tumour is benign.⁴

Schwannomas are often managed non-operatively in asymptomatic cases. However, surgical excision is the treatment of choice for symptomatic cases, cases with uncertain diagnoses and cases in which malignancy is suspected.¹ Submandibular masses, in particular, have an estimated malignancy risk of 22–50%.⁷ The goal of surgical excision is to remove the tumour while preserving the underlying neurological structures.

In this case, CT findings revealed multiple subcentimetre bilateral cervical lymph nodes. While FNA of these lymph nodes could provide cytological insights, its reliability is subject to certain limitations. A literature review indicates that FNA cytology for cervical lymph nodes larger than 1 cm has a non-diagnostic rate ranging from 9.3% to 29.5%.^{8 9} This variability is attributed to factors such as improper handling of aspirates and a lack of qualified cytopathologists, which can result in unsatisfactory samples.

A study by Fu and colleagues focused on ultrasound-guided FNA for small cervical lymph nodes (maximum diameter of 14.6 mm) performed by interventional ultrasound physicians, reporting an inadequate result rate of 5.1%.¹⁰ However, there are no studies specifically examining the efficacy of FNA for cervical lymph nodes smaller than 1 cm without ultrasound guidance.

In our patient’s case, the cervical lymph nodes measured less than 1 cm. Performing FNA would have required specialist consultation for ultrasound-guided procedures, potentially causing treatment delays. In contrast, surgical intervention could be scheduled and performed more promptly, providing both diagnostic and therapeutic benefits. Therefore, we planned a selective neck dissection to obtain histological analysis.

Given the high suspicion of malignancy in the submandibular gland tumour, standard practice recommends selective neck dissection of lymph nodes at levels I–III.¹¹ Accordingly, we performed a right submandibulectomy with cervical lymph node dissection at levels I–IV in this patient.

Histopathological results indicated an ancient schwannoma of the right submandibular gland, which is a rare subtype and location. Similar presentations of ancient schwannomas have been reported in the literature. Bondy et al reported a 25-year-old female patient who presented with pain and swelling in the left submandibular triangle for 6 months. The patient was primarily treated for an infectious disease, but there was no improvement. Finally, the mass was excised and examined under a microscope. Gross examination revealed a tan-brown cystic mass, and microscopic examination revealed mixed areas of dense and loose cellularity. Focal dense areas consist of Verocay bodies and occasionally hyalinised stroma, while loose areas consist of cystic degeneration, defining the characteristics of ancient schwannomas.¹² Ho et al reported a case of a 36-year-old male with a painless, slowly progressive left submandibular gland measuring approximately 4×3 cm in size. The CT tomography revealed a well-defined left submandibular cystic mass with superior and posterior displacements of the submandibular gland. A surgical excision was performed. The histopathological results in this case showed cystic degeneration and nuclear atypia in the Antoni A and B areas. Furthermore, this study confirmed the diagnosis of an ancient schwannoma with strong positive immunostaining for S-100 protein. One-year postoperative follow-up revealed no disease.¹³

Due to the asymptomatic nature of most schwannomas and their rare occurrence in salivary glands, particularly the submandibular gland, the diagnosis of schwannoma in this case was challenging and necessitated the use of multimodal techniques for a definitive diagnosis. This case highlights the crucial role of histopathological findings in confirming the diagnosis of ancient schwannomas. In conclusion, this report illustrates the rare presentation and atypical location of ancient schwannomas.

Patient’s perspective.

Initially, I was concerned about the lump under my right jaw, which appeared spontaneously without pain. However, I worried whether it could be malignant, so I decided to undergo examination. Following consultation with the medical team, it was agreed to proceed with surgery to remove the mass and conduct pathological examination. Postoperatively, there was deviation of the right corner of my mouth, attributed by the physician to a condition that may occur after surgery. Nonetheless, I found solace in knowing that the lump was not malignant. Since then, I have been monitoring my condition, and to date, there have been no recurrences of the lump, and the facial deviation has improved. I am grateful that my condition serves as a case study for interested medical professionals.

Learning points.

• This case report highlights the uncommon occurrence of ancient schwannoma in a less typical location, emphasising the necessity of multimodal techniques in its diagnosis.

• Surgical excision of submandibular gland masses must take into consideration three underlying neurological structures: the marginal mandibular nerve, the lingual nerve and the hypoglossal nerve. Monitoring preoperative and postoperative facial expressions is crucial for optimal patient follow-up care.

• Histopathological examination of ancient schwannoma revealed increased nuclear atypia, which can resemble malignancy and thus should be carefully considered in the differential diagnoses.