Practice Lesson of the Week

When a cyst is not a cyst

BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d2844 (Published 17 May 2011) Cite this as: BMJ 2011;342:d2844
  1. J M Batchelor, specialist registrar1,
  2. S E Handfield-Jones, consultant2
  1. 1Department of Dermatology, Addenbrooke’s Hospital, Cambridge CB2 0QQ
  2. 2Department of Dermatology, West Suffolk Hospital NHS Trust, Bury St Edmunds IP33 2QZ
  1. Correspondence to: J M Batchelor jmb{at}doctors.org.uk
  • Accepted 7 March 2011

Atypical “cysts,” especially painful, enlarging, or unexpected ones, may be malignant and need urgent referral

We present a series of cases in which scalp lesions were diagnosed clinically as cysts, but turned out to be malignant lesions. The cases are relevant to anyone diagnosing or treating skin lesions, as well as to those involved in allocating funding for treatment.

Case reports

Case 1

A 75 year old man presented to his general practitioner with a lump on his scalp. His medical history included aplastic anaemia but he was otherwise well. The GP examined the lump and diagnosed a loculated epidermoid cyst. During excision he found that it adhered to the underlying tissues and so removed it piecemeal. Histological examination of the specimen was difficult because the sample was fragmented, but the lesion was clearly malignant. Plastic surgeons performed a wide excision, and histology showed a tumour with features of a poorly differentiated sebaceous carcinoma.

The differential diagnosis included a metastatic tumour, so extensive investigations were carried out to identify a primary malignancy, but none was found. The patient continued under close follow-up and showed no sign of recurrence 12 months after initial surgery.

Case 2

An 11 year old girl presented to her GP with a three month history of a lump on the back of her head, which was painful and growing larger. The GP made a clinical diagnosis of an epidermoid cyst and referred her non-urgently to the general surgeons. The lesion was thought to be benign, …

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