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Neural Tumours

Pathology of Nerve Sheath Myxoma and Neurothekeoma- Infographics

Dr Sampurna Roy MD                    

 

Dermatopathology Quiz Case 147

Diagnosis: Nerve Sheath Myxoma

Dermatopathology Quiz Case 156

Diagnosis: Cellular Neurothekeoma

 

                                                                                                                      

 

 

Nerve sheath myxoma is a benign soft tissue tumour.

In 1969 Harkin and Reed described an unusual myxoid tumour of probable nerve sheath origin and named it myxoma of nerve sheath.

Later in 1980, Gallager and Helwig described similar lesions as Neurothekeoma.

Cellular neurothekeoma was described by Barnhill and Mihm in 1990.

Recent gene studies strongly supports that, nerve sheath myxomas and neurothekeomas are distinct neoplasms.

Schwann-cell differentiation in the electron microsopic examination of Nerve sheath myxoma cells, suggests an origin from nerve sheath precursor cells.

However, there are still some theories proposing a proliferation of other perineural cells, which brings controversies to the cell of origin.

There are some similar features of Nerve sheath myxoma with other neural tissue tumors, like schwannoma and neurofibroma.

That seems the reason why various names such as pacinian neurofibroma, cutaneous lobular neurofibroma and perineural neurofibroma have been used for this lesion.

Ref: Malkoc M, Ormeci T, Keskinbora M, Yılmaz A, Korkmaz O, Tanik CB. Nerve sheath myxoma of the dorsal paravertebral space. International Journal of Surgery Case Reports. 2014;5(11):858-860. doi:10.1016/j.ijscr.2014.10.003.

Age:  The tumour is usually noted in adolescents and young adults.

Site:  These myxoid lesions are more common on the trunk and lower extremities. Cellular lesions are noted on the head and neck and upper extremities. Some rare cases have been reported in the intracranial, spinal canal, trunk, lower limb and oral cavity.

Clinical presentation: Dome shaped nodule less than 3 cm in diameter. 

Microscopic features:

The tumour is characterized by low cellularity and large amounts of myxoid matrix.

The lesion is usually well circumscribed and diffusely positive for S-100 protein.

The strong positivity of tumor cells for S-100 protein, which is a well-established marker for Schwann cells and myelin sheath, favors the Schwann cell origin.

 

Nonencapsulated, multilobulated and hypocellular tumour, usually located in the reticular dermis and often extends into the subcutaneous fat. 

Tumour is composed of spindle cells, stellate and sometimes epithelioid cells set in a myxoid stroma.   

Spindle cells are arranged in swirling and concentric fashion.

Sometimes multinucleate cells are present.

Focally, there may be nuclear atypia and normal mitotic figures are often present.

Rarely, foci of  ossification and cartilaginous metaplasia have been reported.

Immunohistochemically, the tumour is S100 protein positive.

Differential Diagnosis: Myxoid Tumours of Soft Tissue : The differential diagnoses include schwannoma, neurofibroma, neurilemmoma, leiomyoma, intramuscular myxoma and low-grade sarcoma.

 

 

Further reading:

Malkoc M, Ormeci T, Keskinbora M, Yılmaz A, Korkmaz O, Tanik CB. Nerve sheath myxoma of the dorsal paravertebral space. International Journal of Surgery Case Reports. 2014;5(11):858-860. doi:10.1016/j.ijscr.2014.10.003.

The "neurothekeoma": immunohistochemical analysis distinguishes the true nerve sheath myxoma from its mimics.

Histologic spectrum of neurothekeoma and the value of immunoperoxidase staining for S-100 protein in distinguishing it from melanoma. 

Studies on the cellular origin of neurothekeoma: clinical, light microscopic, immunohistochemical, and ultrastructural observations. 

Neurothekeoma: report of a case in an infant and review of the literature.

 

Cellular Neurothekeoma

Neurothekeoma is a rare, benign, dermal tumour. 

Site, age, sex:

It is mainly located on the face, neck, arms and shoulders of young adults, and is more frequent in females. This lesion should also be suspected in older patients.

Predisposing factors:

Local trauma and estrogen use have been identified as triggering factors. This may explain the 2:1 ratio in females.

Clinical presentation:

It is as an asymptomatic, pink-erythematous, dome-shaped, solitary papule, with a slow growth rate.

Microscopic images:

Multilobular tumour composed of nests and fascicles of spindle or epithelioid cells with vesicular nuclei.

Only focal myxoid change is evident. 

Rarely the tumour may demonstrate infiltrative growth pattern, brisk mitotic activity and cytological pleomorphism.

These atypical features do not influence the prognosis of the tumour.

Depending on the amount of myxoid matrix, Neurothekeoma can be classified into cellular Neurothekeoma (< 10% myxoid matrix), mixed Neurothekeoma (10 - 50% myxoid matrix) and myxoid Neurothekeoma (> 50% myxoid matrix).

Immunohistochemistry: 

Neurothekeoma is almost always positive to melanoma specific antigen (NK1/C-3) and CD10.  PGP9.5 is positive if antigen retrieval method is used.  

The tumour is S-100 protein, HMB-45, Melan-A and CD56 negative. 

It is sometimes positive to smooth muscle actin and neuron specific enolase.

The cell of origin for Neurothekeoma is still unknown.

Nerve sheath myxoma has been often linked to myxoid Neurothekeoma.

It has been argued that Neurothekeoma has nerve sheath differentiation and is part of Nerve sheath myxoma.

Although this remains controversial due to the lack of positive reaction to S-100 protein in all Neurothekeoma variants.

The tumour probably has a fibrohistiocytic origin.

Atypical Neurothekeoma:

An atypical variant of Neurothekeoma (Atypical Neurothekeoma) has recently been described.

Features:

- Larger tumours (upto 6 cm) of deep penetration (skeletal muscle and subcutaneous fat involvement),

- Diffuse infiltrative borders,

- Vascular invasion,

- A high mitotic index (>3 mitosis per 10 high power fields) and

- Pleomorphism.

This variant has been incompletely characterized and its clinical behavior is not entirely understood because of the scarcity of reports.

In a series involving 10 Atypical Neurothekeoma patients, no local recurrence or metastasis was found in 1 to 5 years of follow-up.

It seems that this "histologic aggressiveness" is not correlated with a "clinical aggressiveness".

Still, it is preferable to perform a complete excision of ANT with free margins, until they are more accurately characterized.

Ref:

Atypical or worrisome features in cellular neurothekeoma: a study of 10 cases. 

Atypical neurothekeoma: a new case and review of the literature.  

Atypical cellular neurothekeoma.  

Atypical cellular neurothekeoma a diagnosis to be aware of.  

Differential diagnosis:

Neurofibroma, Schwannoma or neuroma variants ; Fibrohistiocytic tumour and Nerve sheath myxoma.

Spindle cell lesion with atypia and mitotic activity from head and neck area in an elderly individual, which stains positively with S100 protein, is more likely to be Desmoplastic Melanoma.

One should carefully check dermo-epidermal junction. However a junctional component is not always present in Desmoplastic Melanoma.

Ref: Cellular neurothekeoma: case report and its (un) relation with nerve sheath myxoma Anais Brasileiros de Dermatologia. 2015;90 (3 Suppl 1):156-159. doi:10.1590/abd1806-4841.20153402

 

Further reading:

Cellular neurothekeoma: analysis of 37 cases emphasizing atypical histologic features.

Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma arising from the nose.

Cellular 'neurothekeoma': an epithelioid variant of dermatofibroma? 

Cellular neurothekeoma with histiocytic differentiation.

PGP9.5: a marker for cellular neurothekeoma. 

Microphthalmia transcription factor and NKI/C3 expression in cellular neurothekeoma.

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

 


 

 

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