Malignant GIST of the jejunum mimicking periappendiceal abscess

Clinical History

A patient with no past medical history presented at the emergency department with hypogastric pain and fever up to 38ºC. A soft tissue mass was palpated at the hypogastrium during physical examination.
Haematologic tests showed decrease of haematocrit (Ht: 35%) and leucocytosis (16 × 109/L). CEA and CA 19-9 were in the normal range.

Imaging Findings

US revealed an ill-defined mass with heterogeneous echogenicity in the right iliac fossa compressing the urinary bladder. There was no fluid surrounding the mass or in the Douglas space.
On CT a 9×8×6 cm heterogeneous mass with enhancing borders and irregular central areas of fluid and gas was detected in the right iliac fossa without significant lymphadenopathy.
MRI demonstrated a soft tissue mass with areas of central necrosis and gas and fat stranding around it.
A complete resection of the mass that originated in the jejunum and a side to side anastomosis of the small bowel were performed. Due to adhesions with the appendix, an appendicectomy was also performed.
The histopathological examination revealed a malignant GIST with whirling sheets of spindle cells and haemorrhagic necrosis. Immunohistochemical staining for CD117, α-smooth-muscle actin (SMA), and CD34 was positive. On light microscopy there were 9-10 mitoses per 50 high-power fields indicating malignancy of the tumour.

Discussion

Gastrointestinal stromal tumours (GISTs) account for 0.1–3.0% of all GI neoplasms and are classified as spindle cell, epithelioid or pleomorphic mesenchymal tumours. They arise from Cajal interstitial cells and represent the most common mesenchymal neoplasms of the digestive tract. These tumours have been distinguished immunohistochemically from leiomyomas, leiomyosarcomas, leiomyoblastomas or schwannomas. Typical immunohistochemical markers enable the identification of different types of mesenchymal tumours. CD34 protein is present in around 40–70% of all GISTs while CD117 protein is present in nearly all cases. Other markers, such as alpha-smooth muscle actin, show variable expression in 20–30% of GISTs and S100 in about 10% of GISTs.
50-70% of GISTs occur in the stomach; 33% in the small bowel; 5-15% in the rectocolon, and only 1-5% in the oesophagus. Uncommonly, GISTs may also develop as primary tumours of the omentum, mesentery or retroperitoneum.
Patients may present with pain, dysphagia, weight loss, gastrointestinal bleeding, bowel obstruction, or a palpable abdominal mass.
Most GISTs (70–80%) are benign and their diameter ranges from a few millimetres to more than 30 cm. They occur with a small male predominance in persons aged 40-70 years.
20–30% of GISTs are malignant. The risk of malignancy increases with extragastric location, a size greater than 5 cm, extension into adjacent organs, and more than one mitosis per 50 highpower fields. Metastases, if present, extend to the liver or peritoneum. Lymph node enlargement is not a feature.
Differential diagnosis is made with leiomyomas, sharply defined spherical masses with homogeneous or discreet heterogeneous enhancement, most commonly located in the esophagus. Lymphomas are suspected in the presence of a circumferential mural thickening with homogeneous enhancement and/or lymph node enlargement. Carcinoids are found in the terminal ileum and excite a desmoplastic reaction. Carcinomas produce local infiltration and visceral obstruction, especially in large tumours. Metastases are multifocal masses, in a context of primary known malignancy.
As most GISTs have an exophytic growth, CT is more useful than endoscopy and barium studies to evaluate the real size of the tumour and its extension.
Smaller GISTs (< 5 cm) appear as smooth sharply defined intra- extramural masses with uniform, homogeneous attenuation. Larger GISTs (> 5 cm) appear as heterogeneous masses with enhancing borders of variable thickness and irregular central areas of fluid, gas, or oral contrast reflecting necrosis and/or cavitations that communicate with GI lumen. Mucosal ulcerations, intratumoral haemorrhage or segmental dilatation of the bowel may also be seen.
The standard treatment for GIST is surgical resection. High risk GISTs are associated with increased recurrence and decreased survival despite complete surgical resection. These patients should be considered for adjuvant therapy with tyrosine kinase inhibitors.
Using CT, one can only suspect the presence of GIST. Histological diagnosis is always necessary.

Differential Diagnosis List

Final Diagnosis

Malignant GIST of the jejunum

URL:	https://www.eurorad.org/case/9013
DOI:	10.1594/EURORAD/CASE.9013
ISSN:	1563-4086