Abdominal wall mass –MRI Approach

50 yr old lady presents for CEMRI with abdominal wall mass in USG with no history of trauma / fever / surgery.

CEMRI shows –  Large intense & heterogeneously enhancing altered signal intensity space occupying lesion involving left anterior parietes of abdominal wall extending from supraumbilical to pelvic region with areas of necrosis/ restricted diffusion /predominantly edematous signal components /rectus abdominis not separately identified / properitoneal fat stranding with no intraperitoneal extension / across midline /no definite skin ulceration /regional lymphadenopathy / air /MR demonstrable calcification / flow voids leading upto lesion-Not specific to etiology , however, infective or neoplastic etiology like desmoid tumor / lymphoma / pleomorphic sarcoma  / giant cell tumor of tendon sheath /  peripheral nerve sheath tumors / etc. is possible.

Teaching points Submitted by Dr MGK Murthy, Dr GA Prasad

Tumor like lesions of abdominal wall–

-          Abdominal wall endometriosis - defined as endometrial  tissue that is superficial to the peritoneum &  is a common  site of extrapelvic endometriosis that usually develops in  a surgical abdominal scar like  after  caesarean section with  typical presentation of  female patient with cyclical pain  from a solid mass in scar tissue  with iso- to mildly hyperintense on T1W and T2W, with or without small foci of high signal intensity corresponding to hemorrhagic foci & with moderate to intense enhancement.

-          Desmoids tumors - belong to a group of disorders called fibromatoses characterized by fibroblastic proliferation, without evidence of inflammation or definite neoplasia & usually occur in young, gravid women or, more frequently, during the first year after  childbirth. Also association with previous surgery, trauma, estrogen therapy, familial adenomatosis  polyposis, and Gardner syndrome is known. They arise from musculoaponeurotic  structures of the abdominal wall, especially the rectus and internal oblique muscles and their fascial  coverings & usually do not cross the midline. A desmoid tumour does not metastasize but can invade locally  and can recur. Imaging appearance on magnetic resonance imaging (MRI) depends on the stage of pathologic  evolution. Stage 1 is characterized by abundant spindle cells with few areas of collagen and manifests on MRI as low  signal on T1W, high signal on T2W, and homogeneous  contrast enhancement. Stage 2, increasing central and peripheral collagen deposition leads to band-like low signal  intensities on T2W, with these areas showing decreased enhancement. Stage 3  with the increasing fibrous deposition, there is decreased signal on T1W and T2W with decreased contrast enhancement.

-          Abdominal wall hematomas – usually occur in rectus abdominis muscle & result from injury to superior or inferior epigastric arteries. Hematomas usually are infraumbilical and  almost never cross the midline. Appearance on  MRI depends on the stage of the hemorrhage.

-          Epidermoid cysts - rare cystic lesions of ectodermal  origin & usually are congenital but can be acquired after traumatic or  surgical implantation of epidermal elements with well-defined round or ovoid lesions of high signal intensity on T2W MRI and low signal intensity  on TIW images. In many cases, low signal components on  T2W and high signal contents on T1W may be found to  reflect the keratinized debris within these cysts & usually show peripheral enhancement and, occasional  peripheral calcification.

Benign tumors of abdominal wall.

-          Vascular malformations & hemangioma –   They present as lobulated masses  with infiltrative features, a lack of respect for facial planes,  and involvement of multiple tissue types, such as muscle and  subcutaneous fat. Phleboliths are often seen. It is important  to differentiate the high-flow malformations (hemangioma  and arteriovenous malformations) from the low-flow malformations (venous, lymphatic, or mixed).

-          Abdominal wall lipomas .

-          Neurofibromas are benign nerve sheath tumours, with  multiple lesions being the hallmark of neurofibromatosis type 1. Cutaneous manifestations range from small  pedunculated dermal neurofibromas to large diffuse and  plexiform neurofibromas.. They typically are low signal intensity on TIW,  heterogeneously high signal intensity on T2W and show  mild-to-moderate contrast enhancement,  ‘‘Target sign’’ (hyperintense periphery and hypointense  center) and ‘‘split fat sign’’ (rim of fat around tumour) maybe seen on MRI.

-          Subcutaneous leiomyoma - are rare tumours and have  a higher incidence in patients with AIDS. They are more  common in children and young adults, and present as  tender subcutaneous nodules. They are well-circumscribed  single or clustered masses, and are typically iso- to mildly  hyperintense on T1W and heterogeneous high signal intensity  on T2W.

Malignant masses of abdominal wall.

-          Hemangiopericytoma – are slow-growing vascular tumours  of the soft tissue derived from the pericytes of Zimmerman,  which surround capillary walls. They are  well-circumscribed solid hypervascular  tumour, which typically occurs in middle age & show homogeneous and centripetal enhancement early in  the arterial phase . The presence of a vascular  pedicle may be seen occasionally.

-          Dermatofibrosarcoma protuberans is a spindle-cell tumour  that typically arises in the dermis .On imaging, it  presents as a multinodular noncalcified mass that arises from  the skin and extends into subcutaneous tissue with mild to moderate enhancement .  Local recurrence is seen in  20%-55% of cases, and metastases are seen in 5% of cases.

-          Lymphomas  / Sarcomas  / Metastasis  /  Needle tract seedling in RFA – show nonspecific imaging findings with variable signal characteristics  & enhancement.