Several types of lesions have been included under the broad term of “neurothekeoma” (NTK), most commonly nerve sheath myxoma (NSM) and cellular neurothekeoma (CNTK). Over the years, the classification of these tumors has been in a constant state of flux.¹ NSM and CNTK have been classified as benign primary neurogenic tumors arising from peripheral nerves.² NSM was first described as a distinct pathologic entity by Harkin and Reed in 1969 and designated as a benign myxomatous cutaneous tumor believed to be of peripheral nerve sheath origin.³ Gallager and Helwig⁴ later reported a series of cutaneous tumors that bore the same histologic features as the previously described NSM, but which they named NTK. Over subsequent years, the terms “NSM” and “NTK” frequently have been used interchangeably in the literature. In 1986, Rosati et al⁵ described a cellular variant of NSM, termed “CNTK.” However, other studies have questioned the relationship between CNTK and NSM. Some authors supported the idea that these lesions are variants of the same entity.⁶,⁷ Others, however, felt that they are unrelated.⁸,⁹,¹⁰ In 2008, Weiss and Goldblum¹¹ proposed the term “classic NTK” for NSM to distinguish it from CNTK based on immunoreactivity to S-100. While it is generally accepted that a classic NTK is a true benign nerve sheath tumor, the etiology of CNTK remains unknown.⁸,¹⁰

It has been thought by some authors that cellular and myxoid NTK represent two ends of a spectrum of the same neoplasm.⁶,¹²,¹³,¹⁴,¹⁵ According to this view, cellular NTK is considered a neoplasm with immature or poorly developed nerve sheath differentiation, whereas the myxoid type shows well-developed nerve sheath differentiation.³,⁴,⁶,⁸,¹³,¹⁴,¹⁵,¹⁶ Others have questioned this concept, suggesting that cellular NTK should be classified as a fibrohistiocytic tumor and myxoid NTK as a tumor with nerve sheath differentiation.¹⁰,¹⁶,¹⁷,¹⁸

NTKs occur most commonly in the head and neck, especially the nose and scalp. Less frequently, they are seen on the cheeks, chin, eyelids, lower extremities, and trunk.¹⁰,¹⁹ They are seen most commonly in young individuals, ranging in age from 1 to 85 years, with a mean of 21 to 25 years.⁹,¹⁰,²⁰ The male-to-female ratio is approximately 1:2.⁹,¹⁰

NTKs involving the eyelid are often referred to as NTK palpebrae and are very uncommon with less than a dozen cases reported. Slightly more than half of the eyelid cases have been classified as NSMs or classic NTKs,¹,²¹,²²,²³,²⁴,²⁵,²⁶,²⁷ and the rest as CNTKs.²⁸,²⁹,³⁰ Where location was specified, about two-thirds of these lesions occurred in the upper eyelid. The duration of symptoms before presentation ranged from 6 weeks to 8 years.