CASE REPORT by means of gastrotomy. Eighty per cent of foreign bodies in the upper gastro-intestinal tract occur in paediatric patients, followed by edentulous adults, prisoners and psychiatric patients.' Most objects (80 - 90%) pass spontaneously, but 10 - 20% have to be removed endoscopi- cally, and about 1% require surgery," Objects thicker than 2 cm and longer than 5 cm tend to lodge in the stom- ach.' Long foreign bodies (> 10 cm) tend to lodge in the duode- num, where perforations may devel- op. In addition to causing ulceration, bleeding and perforation, it is con- ceivable that they predispose to GOO, as demonstrated in this patient. The spectrum and size of the for- eign body noted on the imaging stud- ies served as the reason for our early recourse to surgery, rather than an- ticipating the spontaneous passage of these foreign bodies. Recurrent episodes of foreign body ingestion may occur, especially in prisoners, psychiatric patients and patients with peptic strictures. References 1. Goldstein SS, Lewis JH, Rothstein R. Intestinal obstruction due to bezoars. Am J Gastroenterol 1984; 79: 313-318. 2. MIT AM, Mir MA. Phytobezoar after vagotomy with drainage or resection. Br J Surg 1973; 60: 846-849. 3. Webb WA. Management of foreign bodies of the upper gastrointestinal tract. Gastro- enterology 1988; 94: 204-206. 4. Schwartz GE Polsky HS. Ingested foreign bod- ies of the oesophagus. Ann Surg 1985; 51: 173- 178. 5. Perelman H. Toothpick perforation of the gas- trointestinal tract. J Abdom Surg 1962; 4: 51-53. 6. Kock H. Operative endoscopy. Gastrointest Endosc 1977; 24: 65-68. A midline naso- pharyngeal cystic structure Thornwaldt's cyst Ralph Drosten MB BCh, FCRad D/ag Department of Thoracic Imaging Brigham and Women's Hospital Boston, USA Case presentation A 39-year-old woman presented to her doctor complaining of a non-pro- ductive cough. On examination, the clinician identified a non-inflamed cystic lesion in the soft tissues of the posterior nasopharynx, slightly to the right of the midline. Magnetic resonance imaging (MRI) examination of the region of interest confirmed a 12 x 11 mm well- defined cystic lesion in the posterior nasopharynx, slightly to the right of centre. It demonstrated a homoge- neously hyperintense signal on T1- weighted images, fat suppression and STIR sequences (Figs 1, 2 and 3). It had a thin wall and did not infiltrate the adjacent soft tissues. 40 SA JOURNAL OF RADIOLOGY. October 2001 On the basis of these imaging characteristics, the diagnosis of a Thornwaldt's cyst was made. Discussion Thornwaldt's cyst is a midline con- genital pouch or cyst, lined by ecto- derm, within the nasopharyngeal mucosal space. It is present in 4% of autopsy specimens and develops from an ectopic portion of notochordal remnants in the nasopharynx. The peak age of presentation is 15 - 30 years.I Clinical symptoms range from it being completely asymptomatic and an incidental finding, to persistent nasopharyngeal drainage, halitosis and a foul taste in the mouth. The pre- senting cough in our patient's case was presumably secondary to nasopha- ryngeal drainage and irritation. MRI is the imaging modality of choice. Cysts measure from 1 to 30 mm in diameter and have a high signal intensity on Tl and T2-weighted images, probably CASE REPORT Figs 1 and 2. T1 and fat suppression saggital MRI images demonstrating a well-defined hyperintense posterior nasopharyngeal midline cystic lesion (arrow). because of proteinaceous fluid con- tent. Thomwaldt's cyst is thought to be a persistent focal adhesion between the notochord and ectoderm extend- ing to the pharyngeal tubercle of the occipital bone. I The notochord rem- nants occasionally give rise to an epithelial tract which empties into the midline of the nasopharynx} This tract may close over and result in a midline cyst which on occasion may become infected. The cyst is usually located in the midline in the longis capitus muscle. Extension off the midline is rarely seen. Secondary infection may lead to a syndrome consisting of prevertebral muscular spasm and postnasal dis- charge. Thornwaldt's abscess must be surgically drained to prevent exten- sion and retropharyngeal abscess for- marion.' The differential diagnosis includes Fig. 3. Coronal STIR image demonstrating 8 retained high signal intensity in the posterior nasopharyngeal midline cystic lesion (arrow). a Rathke's pouch - but this lesion occurs in the craniopharyngeal canal, anterior and cephalad to Thornwaldt's cyst. References 1. Dahnert W. Radiology Review Manual. 3rd ed, Williams and Wilkins, 1996: 295. 2. Higgins CB, Hricak H. Helms C. MR! of the Body. Raven Press. 1992: 368-369. 3. Grainger RG. Allison OJ. Diagnostic Radiology. Vol. 3. Churchill Livingstone, 1999: 2284. 41 SA JOURNAL OF RADIOLOGY. October 2001