Case Reports

Abdominal Wall Schwannoma

Fed Pract. 2019 March;36(3):129-133

References

1. Kransdorf MJ. Benign soft-tissue tumors in a large referral population: distribution of specific diagnoses by age, sex, and location. AJR Am J Roentgenol. 1995;164(2):395-402.

2. Valeyrie-Allanore L, Ismaili N, Bastuji-Garin S, et al. Symptoms associated with malignancy of peripheral nerve sheath tumors: a retrospective study of 69 patients with neurofibromatosis 1. Br J Dermatol. 2005;153(1):79-82.

3. Patterson JW. Neural and neuroendocrine tumors. In: Weedon’s Skin Pathology. 4th ed. Elsevier; 2016:1042-1049.

4. Balzarotti R, Rondelli F, Barizzi J, Cartolari R. Symptomatic schwannoma of the abdominal wall: a case report and review of the literature. Oncol Lett. 2015;9(3):1095-1098.

5. Wasa J, Nishida Y, Tsukushi S, et al. MRI features in the differentiation of malignant peripheral nerve sheath tumors and neurofibromas. AJR Am J Roentgenol. 2010;194(6):1568-1574.

6. Dodd LG, Marom EM, Dash RC, Matthews MR, McLendon RE. Fine-needle aspiration cytology of “ancient” schwannoma. Diagn Cytopathol. 1999;20(5):307-311.

7. Powers CN, Berardo MD, Frable WJ. Fine-needle aspiration biopsy: pitfalls in the diagnosis of spindle-cell lesions. Diagn Cytopathol. 1994;10(3):232-240; discussion 241.

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9. Goldblum JR, Weiss SW, Folpe AL. Benign tumors of peripheral nerves. In: Enzinger and Weiss’s Soft Tissue Tumors. 6th ed. Philadelphia, PA: Elsevier; 2014:813-828.

10. Naversen DN, Trask DM, Watson FH, Burket JM. Painful tumors of the skin: “LEND AN EGG.” J Am Acad Deramatol. 1993;28(2, pt 2):298-300.

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13. Woodruff JM, Selig AM, Crowley K, Allen PW. Schwannoma (neurilemoma) with malignant transformation. A rare, distinctive peripheral nerve tumor. Am J Surg Pathol. 1994;18(9)82-895.

14. Zou C, Smith KD, Liu J, et al. Clinical, pathological, and molecular variables predictive of malignant peripheral nerve sheath tumor outcome. Ann Surg. 2009;249(6):1014-1022.

15. Ahmad RA, Sivalingam S, Topsakal V, Russo A, Taibah A, Sanna M. Rate of recurrent vestibular schwannoma after total removal via different surgical approaches. Ann Otol Rhinol Laryngol. 2012;121(3):156-161.

16. Bhatia RK, Banerjea A, Ram M, Lovett BE. Benign ancient schwannoma of the abdominal wall: an unwanted birthday present. BMC Surg. 2010;10:1-5.

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The neural sheath is made up of 3 types of cells: the fibroblast, the Schwann cell, and the perineural cell, which lacks a basement membrane. It is the Schwann cell that can give rise to the 3 main types of cutaneous nerve tumors: neuromas, neurofibromas, and schwannomas.³ A nerve that is both entering and exiting a mass is a classic presentation for a peripheral nerve sheath tumor. If the nerve is eccentric to the lesion, then it is consistent with a schwannoma (not a neurofibroma).⁴ Schwannomas are made exclusively of Schwann cells that arise from the nerve sheath, whereas neurofibromas are made up of all the different cell types that constitute a nerve. Bilateral vestibular schwannomas (acoustic neuromas) are virtually pathognomonic of neurofibromatosis 2 (NF-2), which can manifest as hearing loss, tinnitus, and equilibrium problems. In contrast, neurofibromatosis 1 (NF-1) is more common, characterized by multiple café au lait spots, freckling in the axillary and groin regions, increased risk of cancers overall, and development of pedunculated skin growths, brain, or organ-based neurofibromas.

Diagnosis

A workup generally includes a thorough history and examination as well as imaging. In cases of superficial subcutaneous lesions, an ultrasound is often the imaging modality of choice. However, magnetic resonance imaging (MRI) and computed tomography (CT) scans are frequently used for more deep-seated lesions. There can be significant differences between malignant and benign neural lesions on MRI and CT in terms of contrast-uptake and heterogeneity of tissue, but the visual features are not consistent. Best estimates for MRI suggest 61% sensitivity and 90% specificity for the diagnosis of high-grade malignant peripheral nerve sheath tumors based on imaging alone.⁵

Definitive diagnosis requires surgical excision. Fine-needle aspiration can be used to diagnose subcutaneous nodules, but there is a possibility that degenerative changes and nuclear atypia seen on a smaller sample may be confused with a more aggressive sarcoma. For example, long-standing schwannomas are often called ancient, meaning that they break down over time, and the atypia they display is a regressive phenomenon.⁶ Therefore, a small or limited tissue sampling may not be representative of the entire lesion.⁷As such, patients will likely need referral for surgical removal to determine the exact nature of the growth.

Although schwannomas are uncommon overall, the highest incidence is in the fourth decade of life with a slight predominance in females. They are often incidentally found as a palpable mass but can be symptomatic with paresthesias, pain, or neurologic changes—particularly when identified in the retroperitoneum or along joints. Schwannomas are most commonly found in the retroperitoneum (32%), mediastinum (23%), head and neck (18%), and extremities (16%).⁸ The majority of cases (about 90%) are sporadic; whereas 2% are related to NF-2.⁹ The abdominal wall schwannoma is rare. Our review of English-language literature in PubMed and EMBASE found only 5 other case reports (Table 1).

On physical examination, superficial lesions are freely movable except for a single point of attachment, which is generally along the long axis of the nerve.

LEND AN EGG is a useful acronym introduced by Naversen and colleagues in 1993 to characterize painful subcutaneous nodules.¹⁰ The acronym is particularly helpful because entities in this acronym are not common and are already difficult to identify as there are frequently no overlying skin changes to help characterize the lesions (Table 2).