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OJHAS Vol. 22, Issue 2: April-June 2023

Original Article
Clinicopathological Spectrum of Schwannoma – A 3-year Retrospective Study with Emphasis on Unusual Sites

Nithya Roopa Prem, Junior Resident,
Swati Sharma, Associate Professor,
Kanthilatha Pai, Professor,
Mary Mathew, Professor and Head of Department,
Department of Pathology, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, Karnataka, India.

Address for Correspondence
Dr. Swati Sharma,
Associate Professor,
Department of Pathology,
Kasturba Medical College,
Madhav Nagar, Manipal-576104
Karnataka, India


Prem NR, Sharma S, Pai K, Mathew M. Clinicopathological Spectrum of Schwannoma – A 3-year Retrospective Study with Emphasis on Unusual Sites. Online J Health Allied Scs. 2023;22(2):6. Available at URL:

Submitted: May 17, 2023; Accepted: July 4, 2023; Published: July 15, 2023


Abstract: Introduction: Schwannoma is a benign neoplasm of neural origin, commonly associated with cranial nerves. The aim of the study is to study the spectrum of demographic and clinical presentation of this neoplasm with special emphasis on unusual sites. We also discuss the histopathological features at these sites and analyse these with the available literature. Materials and Methods: This is a retrospective cross-sectional study of 3 years, where all diagnosed cases of Schwannoma at unusual sites were studied for histopathological parameters along with the clinical and radiological details. Results: 18 cases of Schwannoma at unusual locations were analysed. The age range was 20-82 years with mean age being 45.5 years. The sex ratio was equal. The most common presenting symptom was painless swelling with a duration ranging from 5 days to 7 months. Mean size was 4 cm. The most common site was the head and neck region and lower limbs constituting 28% cases each. All patients underwent complete surgical excision. Clinico-histopathological correlation was 70%. Histopathology confirmed the diagnosis in all cases. Conclusion: Schwannomas are benign lesions with good prognosis and minimal chance of malignant progression. However, the unusual sites and misleading presentations may pose diagnostic challenge for both the clinicians and pathologists alike. The lack of awareness of occurrence of this benign entity at unusual location may lead to unnecessary treatment. Pathologists should keep Schwannoma as a differential diagnosis even if the lesion is present at unusual site.
Key Words: Benign, Neural, Schwann cells, Schwannoma


Schwannomas, also known as neurilemomas are neuroectodermal derived lesions. The cell of origin is Schwann cell, which is responsible for maintaining the myelin coating of neurons.1 Schwann cells are glial cells that provide insulation for both the motor and the sensory neural signal in the peripheral nervous system. They have predilection for sensory nerves with the eighth nerve being most frequently affected.2

Schwannomas are usually isolated, solitary, slow-growing and well encapsulated lesions. In some cases, they are associated with neurofibromatosis syndrome and patients develop multiple Schwannomas, known as Schwannomatosis.1

Aims of the present study are to analyse the spectrum of demographic and clinical presentations of Schwannoma with special emphasis on occurrence at unusual sites, to discuss the histopathological features of this lesion at these unusual locations and analyse with the available literature.

Materials and Methods

A 3-year retrospective cross-sectional observational study was done on 18 diagnosed cases of Schwannoma located at unusual sites after procuring Institutional Ethical Committee Clearance (IEC:15/23). The clinical, radiological and pathological details were retrieved from the hospital records and the pathology database. Parameters described in Table 1 were analysed.

Table 1: Proforma

1. Age

9. Frozen diagnosis if any

2. Gender

10. Gross features

3. Clinical presentation

11. Histopathological diagnosis

4. Size of the lesion

12. Microscopy

5. Site of the lesion

13.Immunohistochemistry, if done

6. Duration

14. Follow up

7. Preoperative radiology

8. Clinical diagnosis


Age and Gender

Of the 18 cases studied, the age ranged from 20- 82 years with a mean age being 45.5 years. Sex ratio was equal.

Site and Size

Head and neck region, and the lower limb were the most common sites, consisting for 28% cases each, followed by 22% cases in abdomen/retroperitoneum region, 16 % cases in thorax, and 6% of cases in the upper limb (Figure 1).

Figure 1: Topographical distribution of the lesion

Clinical presentation

Majority of cases (38 %) presented with painless swelling. Other symptoms included backache (11%), abdominal pain (11%), limb pain (5%). Symptoms like blurring of vision (5%) and reduced hearing (5%) were noted in patients who presented with retro maxillary lesion. The duration of symptoms ranged from 5 days to 6 years.

Preoperative radiology

Imaging was done in 10 cases. Majority of cases underwent magnetic resonance imaging (MRI) (50%) followed by computed tomography (30%), ultrasonography (10%) and radiography (X-ray) (10%). The radiology in all 10 cases were suggestive of benign lesion (Figure 2).

Figure 2: Axial view of CT showing ill-defined heterogenous soft tissue density lesion in right infratemporal fossa (arrow)

Clinical diagnosis

Schwannoma was diagnosed clinically in 7/18 cases. Other suggested clinical diagnosis were paraganglioma, sebaceous cyst and retro-maxillary tumour in one case each. No clinical diagnosis was mentioned in 8 cases. The clinico-histopathological correlation was 70%.

All patients underwent complete surgical excision through relevant approaches.

Pathological Analysis

Frozen was done in 2 cases and were reported as spindle cell neoplasm. Grossly, the lesions ranged 0.5- 15 cm in greatest dimension. Mean size was 4 cm (Figure 3).

Figure 3: Gross - well encapsulated lesion with cystic changes

The microscopic examination of all cases revealed the classic findings of Schwannoma with 33% cases associated with secondary changes like microcytic change, hemosiderin-laden macrophages, foam cells, myxoid change, edema, bizarre nuclei and verocay body formation. In 5/18 cases confirmatory immunohistochemistry S100 was done and found to be positive (Figure 4).

Figure 4: Microscopy - Hypocellular and hypercellular areas H and E (X200), Inset S100 positive(X200)


Schwannomas, also known as neurinomas of Verocay, are slow growing peripheral nerve sheath tumours composed almost entirely of Schwann cells. Other tumours classified as peripheral nerve sheath tumours include neurofibroma, perineuroma, traumatic neuroma and malignant peripheral nerve sheath tumour.1,3–7Neurinomas were first described in 1910, as a group of neurogenic tumours. Later on in 1935, these neurogenic tumours were renamed as 'Neurilemmomas' as it was proposed that they arise from nerve sheath elements.3 Lusk et al stated that highly differentiated perineural cells, the Schwann cell, gives rise to Schwannomas while perineural fibrocytes give rise to more invasive neurofibroma.8 Eventually it was found that the Schwann cell is the common precursor for most nerve sheath tumours, hence named as Schwannoma.3,6

Schwannoma, most commonly occur in patients between age group of 20 - 50 years and only about 12% are seen in the paediatric or adolescent population.9 In our study also, most of the cases were between 3rd – 5th decade. This was also noted in studies done by Gupta et al and Adani et al. 9,10

In present study, equal male to female ratio was found, similar to studies done by Chikkannaiah et al, Akyildiz et al, Majumder et al and Hao et al.11–14 However Gilmer et al and Torossian et al found a female preponderance in their respective case studies. 15,16

The symptoms are mostly related to the tumour location, especially on the sites of weight bearing and pertaining to nerve compression. The usual presenting symptoms ranged from painless swelling to nerve compression symptoms such as tingling, burning sensation, weakness, paraesthesia.13,14 Painless swelling was predominantly the major symptoms in majority of the studies.4,13,14,17 Occurrence of pain and neurological deficit are ominous signs suggestive of malignancy. The unusual symptoms such as nasal obstruction, hoarseness, epiphora, hearing loss, Horner’s syndrome, dysphagia, paraesthesia, pain and respiratory symptoms were noted by few authors based on the site of lesion.18,19The most common clinical presentation in our study was painless swelling.

The spectrum of clinical diagnosis considered by the clinicians other than Schwannoma include ganglion cyst, lipoma, Dupuytren’s contracture, fibroma, hydatid cyst, haemangioma and epidermal inclusion cyst. 14 In present study the other clinical diagnosis suggested by clinicians were epidermal inclusion cyst, retromaxillary tumour and paraganglioma.

Majority of Schwannomas are benign and can occur at a variety of anatomical location. They mostly arise at intracranial site from sensory nerve roots. The most common affected nerve is vestibular branch of the eighth nerve followed by trigeminal nerve. Other lower cranial nerves may be involved in the setting of neurofibromatosis.20 The unusual sites of occurrence documented are parotid, nasopharyngeal region, posterior pharynx, skull base, chest wall, thorax, posterior mediastinum, abdomen, retroperitoneum, pelvis and penis.12,14,19,21–26 In our study the unusual sites reported were retro maxillary region, paraaortic region of the thorax, mediastinum, stomach, retroperitoneum and thigh.

The head and neck region account for 25–45% cases of Schwannomas and usually affect patients in their fifth decade.27 The uncommon site of extracranial Schwannomas in the head and neck include parapharyngeal region, submandibular area, parotid, intraoral and paranasal sinus.27 Arshad et al, in their study diagnosed 9/42 cases Schwannoma at head and neck region. There was no sex predilection and mean age of 30.7 years.18 Leu and Chang et al reviewed a series of 52 cases originating in head and neck region over a period of 8 years where 25 cases occurred in scalp, face, external ear, 9 cases were located in oral cavity/nasal cavity and 18 cases in neck. 17 Head and neck was the most common site in our study as well and constituted 5/18 cases with a mean age of 54.6 years.

In the lower extremity, the usual sites of Schwannoma include posterior tibial nerve and achilles tendon, however this site is affected in <10% of all cases.1,5,28–30 Foot and ankle region are extremely infrequent sites. Kim et al reviewed 397 peripheral nerve sheath tumours, only 8% Schwannomas were located in the lower extremity.31In our study, 5/18 cases were reported in lower extremities at thigh, gluteal lesion and popliteal fossa with a mean age of 48.6 years.

Retroperitoneal location is also extremely uncommon with reported incidence ranging from 0.7 to 2.7%.25 Surendrababu et al reported a rare case of retroperitoneal Schwannoma mimicking ovarian cyst. 32 In our study 4/18 cases were reported in the retroperitoneum region with a mean age of 36 years.

Neurogenic tumours represent 15-25% of mediastinal tumours, generally occurring in the posterior paravertebral area.33 Thoracic neurogenic tumours are generally located in the mediastinum or on the chest wall. Rarely these lesions originate in the lung. Matsumoto et al. reported a 2 cm lesion on the pleura in a 19 year old female which was incidentally detected and was eventually diagnosed as Schwannoma.34 In present study, only 2/18 cases were noted in the thorax region with a mean age of 32.5 years.

Occurrence in the upper extremity is not encountered often. Usually, the ulnar nerve is involved while only 7% of Schwannomas involve the median nerve. In the upper limb, they may be mistaken for ganglion cyst or carpal tunnel syndrome.14 Typically, they appear as swollen, slow-growing lesions along the nerve length. In a study by Tang et al, eight cases of upper-limb Schwannomas were studied with a mean age of 56 years.35 In our study we found only one case in the upper limb region.

Ultrasonography is usually the first imaging modality, and it often reveals a solid, strongly defined, ovoid, homogenous mass. To rule out any bone involvement or anomalies, an X-ray may be taken. Schwannomas often exhibit isointense or decreased signal intensity on T1-weighted images compared to skeletal muscle and heterogeneously elevated intensity on T2-weighted imaging. The target sign, spilt fat sign, and fascicular split sign are some further characteristics of Schwannoma.35 In our study, MRI was performed on majority of cases (50%).

Complete excision is recommended since incomplete resection may result in recurrence.36 Grossly, the lesions are most often spheric or ovoid, firm or rubbery tumours. They range in size from 0.5-15 cm. In our study, grossly the size of the lesion size varied from 1-4 cm. Strauss et al in their study of 28 cases of benign retroperitoneal Schwannoma have reported size range from 5-23 cm and weight range between 0.5-2 kg. 37

The histology of Schwannoma typically shows encapsulated lesion with areas of dense cellularity of aggregated spindle shaped cells arranged short fascicles and bundles termed as Antoni-A regions. Along with hypocellular areas with myxoid matrix termed as Antoni-B regions. Immunohistochemistry is positive for S100 in majority of the cases, vimentin, and neuron-specific enolase are positive, but negative for smooth muscle actin and CD117.13,37,38 Other differentials like solitary fibrous tumour are S100 negative; CD34, CD99 and STAT-6 positive. Paraganglioma are S100 diffusely positive only in sustentacular cells and chromogranin is diffuse positive.13,39,40 The distinction between Schwannoma and neurofibroma is important because the latter shows a small potential for malignant transformation.41 Neurofibromas are not encapsulated and lack the biphasic pattern of Schwannomas. They have a haphazard arrangement of nerve fibres, what is likened to “Shredded Carrot” appearance as opposed to the somewhat oriented nuclei seen in Verocay bodies, a pathognomonic feature of Schwannomas.40

Malignant transformation of Schwannoma account for 5% of peripheral nerve sheath tumours. 4,29,42 The histopathological diagnosis of malignant transformation requires the following criteria: 1. demonstrable areas of benign Schwannoma, 2. unequivocal malignant foci manifested by increased cellularity, numerous mitoses, anaplastic cells and invasiveness, 3. transitional areas between malignant and benign regions.43

Malignant Schwannomas are rare and usually are associated with Von Recklinghausen’s disease. They act as high-grade sarcomas with a high likelihood of producing local recurrence and distant metastasis.23 The histology of malignant component in most of the lesions is of epithelioid morphology.44 However, in our study malignant transformation was not seen in any case during the follow up period of 3 years.


Schwannomas are benign lesion with very good prognosis and have minimal chance of malignant progression. They have predilection for cranial nerves and spinal nerve roots but can occur at unusual sites. These sites and misleading presentations may pose diagnostic challenge for both clinician and pathologists alike. Thus, unawareness of this benign entity can lead to unnecessary treatment. Pathologists must be aware of the occurrence of Schwannoma at unusual sites for the proper management.


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