Rectal Malakoplakia Mimicking Malignancy

A 66-year-old male with diabetes mellitus was referred to the hospital setting due to uncontrolled proctalgia. He denied gastrointestinal bleeding, change in bowel habits and weight loss, and had no relevant alterations in laboratory blood studies. At the physical exam, a bulge in the left lateral rectal wall was detected.

Firstly, a contrast-enhanced CT was performed in the portal-venous phase, which demonstrated a 3.8cm irregular thickening of the left low posterolateral rectal wall. The lesion had a medium density of 60 Hounsfield Units and showed enhancement, which suggested a solid nature. Additionally, there were millimetric adenopathies in mesorectal fat (Figure 1).

Subsequently, an MRI scan was performed for additional characterization, which demonstrated an irregular thickening of the low rectal wall, with a nodular morphology and a craniocaudal extension of 3.8cm, located 2.6cm from anal verge, that exhibited moderate hyperintensity in T1 and T2 and marked diffusion restriction. Furthermore, there was extramural extension and invasion of the mesorectal fascia, and two 7mm adenopathies were identified (Figure 2). Therefore, a presumptive diagnosis of rectal cancer was considered, and staged as T3d, N1, MRF+.

Colonoscopy and repeated biopsies of the mass were performed.

Background

Malakoplakia is a rare, chronic granulomatous disease characterized by impaired phagocytic function of macrophages, leading to a defective response to infection. Various organ systems can be affected and the gastrointestinal tract, mostly rectum and sigmoid colon, is the second most common site of involvement.[1–3]

The pathophysiology of malakoplakia is unclear. Possible mechanisms include infection in immunocompromised patients due to chronic diseases (such as diabetes mellitus) or medication effect.[1] However, there have been case reports in immunocompetent patients.[4,5] Malakoplakia can also be associated with other granulomatous diseases and carcinomas.[5,6]

Clinical Perspective

Clinical presentation of gastrointestinal malakoplakia is unspecific and includes symptoms such as abdominal pain, diarrhoea, gastrointestinal bleeding and bowel obstruction.[1,2,7] However, this condition can be an incidental finding in asymptomatic patients.[2,8,9]

The macroscopic appearance of malakoplakia is variable, and it may appear as mucosal plaques or as nodular, polypoidal or large mass lesions.[7]

In this case, the patient had no other known immunosuppressive condition aside from diabetes mellitus. Infectious diseases testing was negative.

The patient denied associated symptoms besides proctalgia, due to an anal ulcer. On colonoscopy, the lesion appeared as a bulge in the rectal wall.

Imaging Perspective

Imaging characteristics of malakoplakia are variable and nonspecific. There is limited literature concerning gastrointestinal malakoplakia’s radiologic features. Malakoplakia may occur as an irregular thickening or a mass, with heterogenous enhancement and diffusion restriction, similar to malignant lesions.[10] Therefore, malakoplakia is an important differential diagnosis as it can simulate other diseases.

Definite diagnosis is based on histopathological examination, with pathognomonic Michaelis-Gutmann bodies [7], as found in the reported case, with no evidence of malignancy.

Outcome

There is no gold-standard treatment for malakoplakia.[7] Mainstay therapies include antibiotherapy, discontinuation of immunosuppressive treatment, and control of underlying diseases.[2]

In this case, a two-month treatment of trimethoprim-sulfamethoxazole was accomplished. However, due to lesion persistence (Figure 3), the patient underwent additional three months of ciprofloxacin with significant reduction in lesion volume on the last follow-up MRI (Figure 4).

The treatment is usually effective and curative.[1] In some cases, the disease is self-limiting, with spontaneous regression.[2] Therefore, malakoplakia is a benign disease with a good prognosis.

Take Home Message

Malakoplakia is a diagnostic challenge due to its nonspecific findings. This may lead to wrong diagnoses and unnecessary surgical interventions, especially due to similar manifestations with neoplasms. Radiologists must be aware of this condition when formulating the differential diagnosis of colorectal mass lesions, especially in immunocompromised patients, and association with histologic findings is mandatory to reach a diagnosis.

Written informed patient consent for publication has been obtained.