Case Report
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Neurilemoma (Schwannoma) of the ischiorectal fossa: a case report and a brief review of the relevant pathology

Case Report by Johann Coetzee (*) - Amanda De Beer (**)

(*) Krugersdorp Hospital, Krugersdorp, South Africa
(**) Ampath Pathology Laboratories, Kempton Park, South Africa

INTRODUCTION

A case of a primary neurilemoma of the ischiorectal space is described. The ischiorectal fossa is a pelvic anatomic space, which until recently received scanty attention in medical training programmes. With the advent of new surgical techniques in reconstructive pelvic surgery, for example both the trans-obturator route for sub-urethral slings and the passage of trocars for the posterior placement of mesh supports in posterior prolapse, knowledge of the anatomy and pathology of this space has assumed more importance.

A neurilemoma (also spelled neurilemmoma and also referred to as a Schwannoma) of the ischiorectal fossa is very rare. A Pubmed search using neurilemoma, neurilemmoma, Schwannoma and ischiorectal fossa gave no citations, while an advanced Google scholar search came up with two citations, both in male patients. This is therefore to the best of our knowledge the only female patient currently reported in the literature.

CASE REPORT

The patient, a fifty two year old G1 P2 (a set of twins), was referred by her general practitioner with a presumptive diagnosis of a cystic swelling of the left sided Bartholin’s gland. The patient had been aware of the swelling for some three months, but it did not cause pain and there was no bladder or bowel dysfunction. She still had irregular menstrual periods, but had not been sexually active for some time due to a male factor. Clinical examination revealed no abnormalities of the general parameters. There was a large swelling visible and palpable in the area of the left ischiorectal fossa, with delineable margins on vaginal and rectal examination. The rest of the pelvic examination was normal.

Transperineal ultrasound showed that it was not a cystic mass, but a large tumour with a homogenous consistency. The pre-operative diagnosis was that of a lipoma of the ischiorectal fossa.

The tumour was exposed with an incision lateral to the perineum ( Fig. 1 ) photo , and it was easily shelled out with blunt finger dissection.
There was a blood vessel pedicle present in the posterior superior position. The mass ( Fig. 2 ) photo was delivered through the incision and complete haemostasis was obtained in the cavity, which was then obliterated with interrupted sutures. Anatomical structures were sought and care was taken not to place sutures through the rectum or vagina. The post-operative period was uneventful and at the four week follow-up examination the patient had recovered completely.

DISCUSSION

A wide spectrum of disease processes may involve the ischiorectal fossa, including congenital and developmental lesions, inflammatory, traumatic and haemorrhagic conditions; primary tumours and pathologic processes from outside the ischiorectal fossa with secondary involvement.Clinical examination, transperineal ultrasound, computed tomography and magnetic resonance imaging are all useful in the diagnosis of these conditions.1

Neurilemomas, or Schwannomas, derive from the Schwann cells of nerve sheaths, and may occur singly or multiply on any nerve or nerve root. The most common location is in fact the acoustic nerve, making this a frequent intracranial tumour. Neurilemomas are almost always benign, very infrequently malignant and should then be called neurogenic sarcomas. However, even benign lesions may recur after incomplete removal. Neurilemomas generally appear in middle adult life but sometimes are encountered earlier, particularly in association with von Recklinghausen’s neurofibromatosis.

This hereditary syndrome is characterized by multiple nerve tumours, either neurofibromas or neurilemomas.2 Histologically two patterns, so called Antoni A and Antoni B are encountered in neurilemomas. The Antoni A pattern comprises interlacing bundles or whorls of elongated spindle cells, and the Antoni B pattern a very loose, disorganized myxoid tissue with abundant ground substance and scattered stellate cells. Both histological patterns were present in the tumour resected from our patient ( Fig. 3 ) photo , and staining for protein S100 was positive.

CONCLUSION

Neurilemoma are mostly resectable curable growths3 and with careful attention to complete excision and the surrounding anatomy the prognosis will be excellent.

REFERENCES

  1. Llauger J, Palmer J, Perez C, et al. The normal and pathologic ischiorectal fossa at CT and MR imaging. RadioGraphics 1998; 18: 61-82.
  2. Woodruff JM. Pathology of the major peripheral nerve sheath neoplasms. Monogr Pathol 1996; 38: 129-161.
  3. Miller M, Kulaylat MN, Ferrario T, Karakousis CP. Resection of tumors of the ischiorectal fossa. J Am Coll Surg 2003; 196: 328-332.

Correspondence to: Johann Coetzee
Krugersdorp Hospital,
Krugersdorp, South Africa.
E-mail:johcc@iafrica.com