Teaching Case

A 31-year-old female patient was admitted to the hospital for fever, pelvic pain and painful defecation of three days´ duration. Abdominal palpation revealed tenderness over the lower quadrants and a palpable retrovaginal mass.

The patient presented with fever, pelvic pain and painful defecation for three days. No vaginal discharge was reported. She had a vaginal delivery eight months ago.
Physical examination revealed painful pelvic palpation and a palpable retrovaginal mass.
WBC count was 16.5X109/L (4-11x109), RCP was 9.2mg/dL (<0,5) and β-hCG<1mU/mL (<1).
Transabdominal ultrasound showed a cystic lesion, with uniform low-level echoes, posterior to the vagina (Fig. 1).
A CT examination was performed and confirmed the presence of a multiloculated cystic lesion, with thick enhancing walls, located in the perirectal compartment, with extension to right ischiorectal fossa (Fig. 2). The CT density of the lesion was within the water range (-5 to 0HU), both before and after contrast material administration.
The lesion exerted mass effect in the cervix and the vagina and compression of the rectum, without invasion.
An MR study revealed four complex cystic lesions, with no communication between them (Fig. 3). The major one measured 15 x 10cm, had irregular thickened margins, low-signal intensity on T1-weighted images and high signal-intensity on T2-weighted images. Posterior to this, there were two lesions with heterogeneous content, with areas of medium-signal intensity on T1 and T2-weighted images. A small lesion showed high signal-intensity on T1-weighted images and low signal-intensity on T2-weighted images. Uterus and the ovaries were normal.
The preoperative diagnosis based on the combination of clinical-laboratory data and imaging findings was that of a benign lesion, probably of infectious origin.
The patient underwent paravulvar incision and the mass was resected (Fig. 4). The pathological diagnosis was an infected mature cystic teratoma.

Teratomas are neoplasms that originate in pluripotent cells and are composed of a wide diversity of tissues foreign to the anatomic site of origin [1]. The etymology of the term (from the Greek “teraton”, a monster) suggests the notion of disturbed development.
They are most frequently found in the gonads, during the reproductive years.
Extragonadal teratomas are rare; they arise from remnants of the genital ridge and mainly occur in or near the midline [1].
The most common sites of extragonadal teratomas are the anterior mediastinum and the sacrococcygeal region.
Mature teratomas are commonly cystic tumours composed exclusively of mature, adult-type tissues. Malignancy behaviour is expected upon the findings of primitive, undifferentiated cells and the proportion of immature tissues within the tumour [2] or as the malignant transformation of adult type tissues.
At CT the fatty elements display characteristic low attenuation, which is pathognomonic. Solid parts and calcifications are typical.
MRI findings include sharply delineated lesion with high SI on T1-weighted images and loss of signal on the fat-saturated T1-weighted images.
Torsion, tumour rupture and infection are possible complications. Torsion of the pedicle is responsible for acute abdominal pain and may be associated to infarction, perforation or intra-abdominal haemorrhage. Tumour rupture (1% of cases) can be spontaneous or traumatic. The spillage of the cyst contents into the abdominal cavity produces chemical peritonitis with granulomatous nodules mimicking tuberculosis or carcinomatosis. Infection of the tumour is reported in 1% of cases [2].

The differential diagnosis includes development cysts (tail-gut and duplication), perirectal collections, cystic lymphangioma, pseudomyxoma retroperitonei, sacrococcygeal teratoma and anterior sacral meningocele [4, 5].
Tail-gut cyst is a presacrococcygeal multilocular cystic mass, derived from a single germ cell layer and should be excluded by the histological findings.
Rectal duplication cyst is in continuity with the rectum, has dual layer of smooth-muscle and a mucosal lining.
Abscess and haematoma often result from postoperative conditions; however, a chronic abscess cavity may reveal a developmental cyst.
Cystic lymphangioma is more frequently encountered in children and in cervical location; occurrence in a subperitoneal pelvic location is rare. It appears as a well defined, multicystic lesion with thin septa, lined with endothelium and filled with a clear fluid.
Pseudomyxoma retroperitonei is a rare condition, composed of cysts lined with glandular epithelium and gelatinous content.
Sacrococcygeal teratomas are germ cell tumours, mostly diagnosed in the newborn period, as a large exophytic sacral mass, usually benign. Rarely, they are discovered in adult life and are completely presacral (type IV). At CT or MRI, they appear as well-defined lesions, with mixed cystic and solid components, uncommonly entirely cystic [6].
Anterior sacral meningocele is a meningeal outpouching communicating with spinal subarachnoid space through a defect in the sacrum [4].

In our case, the signal intensity of each cyst represents different components. The thickened wall and the intermediate signal intensity content are related to infection; the high SI on T1-weighted images represents sebaceous material.
The differential diagnosis included: infected collection (heterogeneous content), cystic lymphangioma (multilocular appearance) and sacrococcygeal teratoma (fatty components).
However, surgical excision was indicated to establish the diagnosis and to exclude malignancy.