Teaching Case

A 75-year-old female presented to the surgery emergency with chief complaints of pain abdomen with distension, shortness of breath, loss of weight and appetite for 2 months. No history of altered bowel habitus, melena or haematemesis was given. Lower abdomen appeared rigid with a palpable hard mass. Laboratory tests revealed raised CA-125 levels (350 IU/L).

A transabdominal ultrasound (US) revealed a large heterogeneously hyperechoic mass in the pelvis reaching up to the abdomen. It was closely abutting the uterus with non-separate visualization of the right ovary.  Color Doppler showed vascularisation within the mass. (Figure 1) Mild ascites and moderate right pleural effusion were also noted.

Non contrast computed tomography scan(NCCT) with oral contrast revealed a large pelvic mass abutting the uterus and bowel loops. The right ovary was not separately visualized from the mass. No area of calcification or hemorrhage noted within the mass. (Figure 2)  The left ovary appeared normal. Contrast-enhanced computed tomography (CECT) scan showed heterogeneous enhancement with multiple non- enhancing cystic/necrotic areas within the mass. (Figure 3) In view of clinical presentation, raised CA-125 levels, radiological non-separate visualization of the right ovary, ascites and right pleural effusion possibility of ovarian malignancy was considered.

Exploratory laparotomy of the patient revealed a large mass arising from the jejunum and extending exophytically into the pelvis which was histopathologically proven to be Gastrointestinal stromal tumor (GIST).(Figure 4)

GIST is mesenchymal tumor of the gastrointestinal tract arising from the Interstitial cells of Cajal. It can arise from any part of the gastrointestinal tract most commonly being stomach (70%), however, it can also originate from retroperitoneum, omentum, and mesentery. They express CD117 (95%) & followed by CD34 (70%). [1, 2]

It usually occurs around the fourth to the sixth decade of life with varying clinical presentations depending upon the site of origin like haematemesis, abdominal pain, distention, anorexia, and weight loss. [3]

Sonographically GISTs can have nonspecific appearance depending upon areas of necrosis and hemorrhage within. Large GISTs presenting as pelvic masses may mimic more commonly encountered gynecological entities like uterine myomas or ovarian malignancies. [4]

On CECT GISTs may appear as heterogeneously enhancing well-circumscribed masses with internal non-enhancing areas of necrosis and calcifications. Owing to their exophytic pattern of growth they present as abdominopelvic masses of varying sizes abutting adjacent organs causing difficulty in determining organ of origin. There are few case reports in the literature where a pelvic GIST was misdiagnosed as degenerated leiomyoma, ovarian fibroma, or mature cystic teratoma. [5] Few radiological signs like positive embedded organ sign (organ of origin invaginates into the mass instead of being compressed externally by the mass) or beak sign (mass deforms the edge of its organ of origin into a beak shape) may help to determine the gastrointestinal origin of GIST. [3, 6]  Sometimes a small band of tissue can be seen connecting the mass to the organ of origin. [6] No such band was visualized in our case. Another diagnostic tool used is phantom organ sign which states that if a larger mass is originating from a smaller organ it can completely obscure the organ of origin making it invisible. [7] However, this was misleading in our case probably due to small and atrophic ovary in the postmenopausal female which may have been obscured by adjacent large non-ovarian mass giving a false positive sign. GISTs may rupture intraperitoneally presenting with ascites and peritoneal metastasis mimicking ovarian malignancies. [8]

GISTs respond to chemotherapeutic tyrosine kinase inhibitors thereby decreasing their preoperative size and risk-off recurrence, thus stressing the need for correct preoperative diagnosis.

To conclude GISTs due to lack of typical radiological presentations and exophytic patterns of growth have always been a diagnostic dilemma. Laboratory markers like raised CA-125 can be fallaciously elevated misleading the diagnosis. Phantom organ sign can be falsely positive in postmenopausal females in relation to the ovaries. GIST must be considered in differential diagnosis of patients presenting with atypical abdominal-pelvic masses where organ of origin cannot be easily delineated.

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