Psammomatous Melanotic Schwannoma

Last Updated October 18, 2011

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Schwannomas are encountered in the gastrointestinal tract with the most commonly affected site being the stomach [1-3]. However, cases have also been documented within the colon [4-6]. The histological spectrum that may be encountered in schwannomas can vary widely but psammomatous melanotic schwannoma is a characteristic lesion that is often seen in association with Carney’s complex [7]. Carney first described this unique variant of schwannoma in 1990 which he noted in peripheral and posterior spine nerve roots near the midline, bone, soft tissue, heart, liver, skin, bronchus, retroperitoneum and the gastrointestinal tract [7].

In a series of 20 schwannomas of the colorectum, Miettinen et al noted that there was an equal gender distribution, wide age range (18-87 years; mean 65 years), size ranging from 0.5 to 5.5 cm, most frequently seen in the cecum followed by sigmoid and rectosigmoid, then transverse colon, descending colon and rectum only [4]. The schwannomas appear as polypoid lesions causing bleeding, obstruction and abdominal pain. The commonest pattern seen consists of spindle cells with Verocay body formation. The epithelioid variant, interestingly, occurred most frequently in the descending and sigmoid colon. These tumors were S100 positive but CD34 and CD117 negative and all behaved in a benign fashion.

Melanin pigment has been described in schwannomas [8] and amianthoid type calcification has also been encountered. The combination of melanin pigment and psammomatous calcification within a schwannoma occurs in two settings.  Schwannomas, thus characterized, are associated with Carney’s complex, which is named for Aidan Carney who first described the constellation of features attributed to this disease. It is a multiple neoplasia and lentiginosis syndrome of variable expression and nearly complete penetrance [9-11]. The complex consists of myxomas in the heart, breast, uterus and skin, lentigines, endocrinopathy (Cushing’s syndrome from a bilateral pigmented nodular adrenocortical hyperplasia or acromegaly) and a variety of tumors including psammomatous melanotic schwannoma, growth hormone-producing pituitary adenomas, epithelioid blue nevi, calcifying large cell Sertoli cell tumor of testis, tumors of the thyroid and ductal adenoma of the breast [12-14]. In a detailed analysis of 40 psammomatous melanotic schwannomas Carney noted that several cases occurred without the features of the complex [7]. Those that were associated with Carney’s complex tended to be younger with an average age of 20 years, whilst those without the complex were around 33 years of age. There was an equal frequency of tumors in the gastrointestinal tract with or without the complex.  He also noted that the tumors may precede the onset of the complex. Within the gastrointestinal tract these tumors occurred from the esophagus to the rectum with the majority occurring in the stomach [7].

Microscopically, they are composed of solid sheets of spindled, dendritic and epithelioid cells. The nuclei vary from being fusiform to round with vesicular of hyperchromatic chromatin, small nucleoli and occasional nuclear pseudo-inclusions [7]. In occasional cases, the nuclei may be large and binucleate, trinucleate and even cells with 10 or more nuclei may be encountered. The cytoplasm is generally eosinophilic and melanin is present in variable amounts. Verocay bodies are unusual. The psammomatous calcification tends to be round or oval and occasional mulberry shaped foci are present. The psammoma bodies are scattered relatively uniformly throughout the tumors. Approximately, 50% of psammomatous melanotic schwannomas may also contain areas of fat. Osseous metaplasia and thick walled vessels may also be noted. Overt cytological atypia is not seen and very occasional to rare mitotic figures are noted [7].

The differential diagnosis includes primary or metastatic melanoma, gastrointestinal stromal tumour (GIST), pigmented neuroendocrine tumour and epithelioid leiomyoma. The absence of cytological atypia (mitoses, large inclusion-like nucleoli, hypercellularity and foci of necrosis) militates against a diagnosis of melanoma despite the melanoma immunohistochemical markers being positive. A psammomatous malignant melanoma has been described [16]. These authors reasoned that their lesion (which had neural-like features) was a melanoma on the basis that the lesion arose within an intradermal nevus, displayed a high mitotic rate, showed necrosis and marked pleomorphism in the deep aspects of the tumour [15]. GIST, pigmented neuroendocrine tumour and epithelioid leiomyoma have a characteristic immunophenotype that allows distinction from a psammomatous melanotic schwannoma.

 

This case highlights an unusual presentation of a rare tumour, a psammomatous melanotic schwannoma presenting as incidental colonic polyps in an asymptomatic patient who lacked the stigmata of Carney’s complex.

 

References

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  2. Prevot S, Bienvenu L, Vaillant JC, de Saint-Maur  PP (1999)  Benign schwannoma of the digestive tract: a clinicopathologic and immunohistochemical study of five cases, including a case of esophageal tumor.  Am J Surg Pathol 23:431-436
  3. Sarlomo-Rikala M, Miettinen M (1995)  Gastric schwannoma: clinicopathologic analysis of six cases.  Histopathology 27:335-340
  4. Miettinen M, Shekitka KM, Sobin LH (2001)  Schwannomas of the colon and rectum.  A clinicopathologic and immunohistochemical study of 20 cases.  Am J Surg Pathol 27:846-855
  5. Skopelitou AS, Mylonakis EP, Charachanti AV, Kappas AM (1998)  Cellular neurilemmoma (schwannoma) of the descending colon mimicking carcinoma: report of a case.  Dis Colon Rectum 41:1193-1196
  6. Tomozawa S, Masaki T, Matsuda K, Yokoyama T, Ishida T, Muto T (1998)  A schwannoma of the cecum: case report and review of the Japanese schwannomas in the large intestine.  J Gastroenterol 33:872-875
  7. Carney JA (1990)  The psammomatous melanotic schwannoma.  A distinctive, heritable tumor with special associations, including cardiac myxoma and the Cushing syndrome. Am J Surg Pathol 14:206-222
  8. Culhaci N, Dikicioglu E, Meteoglu T, Boylu S (2003)  Multiple melanotic schwannoma.  An Diagn Pathol 7:254-258
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  11. Veugelers M, Wilkes D, Burton K, McDermott DA, Song Y, Goldstein MM, La Perle K, et al (2004)  Comparative PRKAR1A genotype-phenotype analyses in humans with Carney complex and prkar1a haploinsufficient mice.  Proc Natl Acad Sci 101:14222-4227
  12. Wilkes D, McDermott DA, Basson CT (2005)  Clinical phenotypes and molecular genetic mechanisms of Carney complex.  Lancet Oncol 6:501-508
  13. Carney JA, Toorkey BC (1991)  Ductal adenoma of the breast with tubular features.  A probable component of the complex of myxomas, spotty pigmentation, endocrine over activity, and schwannomas.  Am J Surg Pathol 15:722-731
  14. Carney JA, Young WF (1992)  Primary pigmented nodular adrenocortical disease and its associated conditions.  The Endocrinologist 2:6-21
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