Mesenchymal Hamartoma of the Chest Wall: Radiologic Manifestations with Emphasis on Cross-sectional Imaging and Histopathologic Comparison1

¹ From the Dept of Radiology, Walter Reed Army Medical Center, Washington, DC (K.R.G.); the Depts of Radiologic Pathology (M.D.M., G.J.L., M.L.R.d.C.) and Orthopedic Pathology (L.M.H.), Armed Forces Institute of Pathology, Washington, DC; Dept of Radiology and Nuclear Medicine, Uniformed Services University of Health Sciences, Bethesda, Md (M.D.M., G.J.L., M.L.R.d.C.); Dept of Radiology, University of Maryland School of Medicine, Baltimore (M.D.M.); and the Dept of Radiology, Chesapeake General Hospital, Va (A.H.T.). From the 1998 RSNA scientific assembly. Received Feb 28, 2001; revision requested Apr 2; revision received Jun 26; accepted Jul 5.

	ABSTRACT

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To describe the imaging features of chest wall mesenchymal hamartoma with emphasis on cross-sectional imaging and comparison with histopathologic results.

MATERIALS AND METHODS: For 14 mesenchymal hamartomas of the chest wall in 12 children, radiologic studies (computed tomographic [CT] scans [n = 14], radiographs [n = 11], magnetic resonance [MR] images [n = 9], and bone scintigraphic images [n = 1]) were reviewed by four radiologists with consensus agreement. Clinical history was reviewed for patient demographics and symptoms at presentation. Radiologic studies were evaluated for lesion location, size, number of affected ribs, cortical irregularity or erosion, presence and type of matrix mineralization, lung hyperaeration adjacent to the lesion, degree and homogeneity of radionuclide uptake, and intrinsic characteristics on CT and MR images.

RESULTS: Patients included seven male and five female children. Nine patients (75%) were younger than 1 year. Five patients had a chest wall mass; in the remaining seven, the lesion was discovered incidentally. All 14 lesions arose from ribs, 11 were located posteriorly, and 11 affected multiple contiguous ribs. Two patients had multifocal disease, each with two discrete lesions. Radiography in all cases revealed a large expansile rib lesion and an associated extrapleural soft-tissue mass, suggesting an aggressive process. Mineralization was seen in seven (64%) lesions at radiography and in 14 (100%) lesions at CT. Hemorrhagic cavities (secondary aneurysmal bone cyst regions) were common, seen in nine (64%) lesions at CT and in four (80%) of five lesions imaged with T2-weighted MR imaging.

CONCLUSION: Mesenchymal hamartoma of the chest wall may be recognized by its characteristic occurrence in infancy and cross-sectional imaging features of mineralization and hemorrhagic cystic (secondary ABC) components.

　

Index terms: Hamartoma, 471.319 • Neoplasms, in infants and children, 471.319 • Ribs, abnormalities, 471.319 • Ribs, neoplasm, 471.319

	INTRODUCTION

Top ABSTRACT INTRODUCTION ATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Mesenchymal hamartomas of the chest wall are rare lesions of early infancy and childhood; approximately 60 cases had been reported at the time this article was written. Mesenchymal hamartomas always arise in the rib and constitute benign proliferations of skeletal tissue characterized by a prominent cartilaginous component and hemorrhagic cavities (secondary aneurysmal bone cyst ). Whereas the most common manifestation is a deforming chest wall mass often noted at birth, many lesions are discovered incidentally on chest radiographs obtained during the evaluation of respiratory symptoms. Patients with large intrathoracic mesenchymal hamartomas may rarely have severe, and sometimes fatal, respiratory compromise (1,2).

The typical radiographic manifestation of a chest wall mesenchymal hamartoma is that of a large, extrapleural, partially calcified soft-tissue mass arising from one or more ribs, with associated destruction and distortion of the adjacent osseous thorax. Although these features suggest an aggressive process, mesenchymal hamartomas are benign lesions, with no reports of recurrence or metastasis following complete surgical resection (2).

The largest series of mesenchymal hamartomas of the chest wall published at the time this article was written described only radiographic features in six of nine cases (1). In 1993, Ayala et al (3) reported the radiologic features of mesenchymal hamartoma of the chest wall in five new cases, four with radiography and one with computed tomography (CT). Additional isolated case reports of one to four patients have included radiographs (4–8), CT scans (4,5,7–9), and magnetic resonance (MR) images (4,5,7,8). In two cases, mesenchymal hamartoma of the chest wall was initially visualized as a chest wall mass in a fetus during prenatal ultrasonography (4,9).

The purpose of our study was to describe the imaging features of chest wall mesenchymal hamartomas, with emphasis on cross-sectional imaging and comparison with histopathologic results. We reviewed the images of 12 patients with a total of 14 mesenchymal hamartomas of the chest wall, to the best of our knowledge the largest series described to date.

	MATERIALS AND METHODS

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
We retrospectively reviewed 14 cases of mesenchymal hamartomas occurring in 12 patients from the archives of the Armed Forces Institute of Pathology (AFIP). This study was performed with the approval of the AFIP Human Subjects Committee. Informed consent was not required.

Multifocal involvement was present in two patients, each showing two separate distinct lesions. In one of these patients, both lesions were confirmed as mesenchymal hamartoma at histopathologic examination after biopsy. In the second patient, biopsy was performed of only the anterior lesion. Given similar imaging characteristics, the second, posterior lesion was presumed to represent a mesenchymal hamartoma as well, but biopsy of this lesion was not performed. The solitary lesions that occurred in the 10 remaining patients were all confirmed as mesenchymal hamartomas at histopathologic examination.

Radiologic studies of each lesion were reviewed by two musculoskeletal (M.D.M., A.H.P.), one pediatric (G.J.L.), and one thoracic (M.L.R.d.C.) radiologist together with consensus and included CT (n = 14 [six with intravenously administered contrast material enhancement, six without, and two with and without contrast material enhancement]), radiography (n = 11), MR imaging with high-field (1.5-T) units in five patients and with low-field (0.3-T) units in two (n = 9 [T1-weighted images, n = 9; T2-weighted images, n = 5; intravenously administered gadolinium-enhanced T1-weighted images, n = 4]), and bone scintigraphy (n = 1). For T1-weighted MR imaging, the repetition time (TR) was 459–800 and the echo time (TE) was 16–29; for T2-weighted imaging, the TR was 1,778–3,200 and the TE was 80–120.

Clinical histories were reviewed, including patient age, sex, and clinical presentation. Radiographs were evaluated for lesion location and size, number of affected ribs, and presence or absence of cortical irregularity or erosion. Matrix mineralization was assessed on the radiographs and CT scans and classified as chondroid if characterized by arcs and rings or osteoid if cloudlike or amorphous. The presence or absence of hyperaeration in the lung adjacent to the lesion was evaluated on CT scans, although only four cases had scans with lung window settings available for review. The presence or absence of an extrapleural mass was assessed on radiographs, CT scans, and MR images. Cystic components were identified on CT scans as regions of low attenuation and on MR images as areas of homogeneous low signal intensity on T1-weighted images and of high signal intensity on T2-weighted images. Enhancement pattern and degree were not adequate to evaluate on CT scans in the two cases with images obtained both before and after administration of contrast material. Hemorrhagic elements within the cystic regions (secondary ABC areas) were identified on CT scans by the presence of fluid levels and on MR images as areas of high signal intensity on either T1-weighted images alone or both T1- and T2-weighted images, and/or the presence of fluid levels. MR images were evaluated for predominant signal intensity characteristics (low, intermediate, high), signal homogeneity or heterogeneity, as well as enhancement characteristics (degree and pattern) after the intravenous administration of a gadolinium-based contrast material. On T1-weighted images, low signal intensity was defined as signal intensity less than that of muscle; intermediate signal intensity, similar to that of muscle; and high signal intensity, similar to that of fat. On T2-weighted images, low signal intensity was defined as signal intensity similar to that of muscle; intermediate signal intensity, similar to that of fat; and high signal intensity, greater than that of fat. Skeletal scintigraphic images obtained with technetium 99m–labeled diphosphonate were evaluated for degree and homogeneity of uptake of the radiotracer in the lesion.

Pathologic material was evaluated by a skeletal pathologist (L.M.H.) to confirm diagnosis; describe histologic components, including matrix composition and presence of hemorrhagic cavities (secondary ABC regions); and exclude features of malignancy.

	RESULTS

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The patients included seven boys and five girls aged 1 day to 13 years, with an average age of 18 months (Table). Nine (75%) of the 12 patients were younger than 1 year. Seven (58%) patients presented with respiratory symptoms (cough, fever, tachypnea), and the rib mass was discovered incidentally. The remaining five (42%) patients had obvious deformities of the chest wall, noted at birth in four of the five (Fig 1) and at age 13 months in the fifth.

fig.ommitted Characteristics of Mesenchymal Hamartoma of the Chest Wall

 

fig.ommitted   Figure 1a. Mesenchymal hamartoma of the chest wall in a newborn boy. The lesion was discovered at birth because of a large left-sided chest wall mass, and biopsy was performed. The mass progressively enlarged over the subsequent 2 months, leading to surgical resection, although there were no respiratory symptoms. (a) Clinical photograph obtained at age 2 months shows large protuberant chest wall mass (arrow). (b) Anteroposterior radiograph shows a large mass involving multiple contiguous left ribs, with faint chondroid mineralization (arrowhead) medially. (c) Sagittal nonenhanced T1-weighted MR image (800/17) reveals high-signal-intensity foci (arrows) representing hemorrhagic cavities. (d) Sagittal gadolinium-enhanced T1-weighted MR image (600/20) shows lack of enhancement (arrowheads) in cystic regions. Other noncystic (solid) areas reveal diffuse enhancement.

 

fig.ommitted Figure 1b. Mesenchymal hamartoma of the chest wall in a newborn boy. The lesion was discovered at birth because of a large left-sided chest wall mass, and biopsy was performed. The mass progressively enlarged over the subsequent 2 months, leading to surgical resection, although there were no respiratory symptoms. (a) Clinical photograph obtained at age 2 months shows large protuberant chest wall mass (arrow). (b) Anteroposterior radiograph shows a large mass involving multiple contiguous left ribs, with faint chondroid mineralization (arrowhead) medially. (c) Sagittal nonenhanced T1-weighted MR image (800/17) reveals high-signal-intensity foci (arrows) representing hemorrhagic cavities. (d) Sagittal gadolinium-enhanced T1-weighted MR image (600/20) shows lack of enhancement (arrowheads) in cystic regions. Other noncystic (solid) areas reveal diffuse enhancement.

 

fig.ommitted Figure 1c. Mesenchymal hamartoma of the chest wall in a newborn boy. The lesion was discovered at birth because of a large left-sided chest wall mass, and biopsy was performed. The mass progressively enlarged over the subsequent 2 months, leading to surgical resection, although there were no respiratory symptoms. (a) Clinical photograph obtained at age 2 months shows large protuberant chest wall mass (arrow). (b) Anteroposterior radiograph shows a large mass involving multiple contiguous left ribs, with faint chondroid mineralization (arrowhead) medially. (c) Sagittal nonenhanced T1-weighted MR image (800/17) reveals high-signal-intensity foci (arrows) representing hemorrhagic cavities. (d) Sagittal gadolinium-enhanced T1-weighted MR image (600/20) shows lack of enhancement (arrowheads) in cystic regions. Other noncystic (solid) areas reveal diffuse enhancement.

 

fig.ommitted Figure 1d. Mesenchymal hamartoma of the chest wall in a newborn boy. The lesion was discovered at birth because of a large left-sided chest wall mass, and biopsy was performed. The mass progressively enlarged over the subsequent 2 months, leading to surgical resection, although there were no respiratory symptoms. (a) Clinical photograph obtained at age 2 months shows large protuberant chest wall mass (arrow). (b) Anteroposterior radiograph shows a large mass involving multiple contiguous left ribs, with faint chondroid mineralization (arrowhead) medially. (c) Sagittal nonenhanced T1-weighted MR image (800/17) reveals high-signal-intensity foci (arrows) representing hemorrhagic cavities. (d) Sagittal gadolinium-enhanced T1-weighted MR image (600/20) shows lack of enhancement (arrowheads) in cystic regions. Other noncystic (solid) areas reveal diffuse enhancement.

 
All lesions arose from ribs. The posterior ribs were affected in 11 (79%) lesions. Radiographs in all cases demonstrated a large expansile rib lesion with cortical irregularity and erosion, and an extrapleural soft-tissue mass. Lesions were 2 x 2 cm to 10 x 15 cm in diameter, with an average diameter of 5.2 x 3.5 cm. Multiple contiguous ribs were affected in 11 (79%) of 14 lesions, whereas three (21%) lesions involved only one rib. Seven (64%) of 11 lesions demonstrated matrix mineralization on radiographs, with six (86%) of the seven having a chondroid appearance (Figs 1, 2). Mineralization appeared osteoid in one (14%) lesion, in which bone scintigraphy demonstrated mild homogeneous uptake of radiotracer in the lesion.

fig.ommitted Figure 2a. Mesenchymal hamartoma of the chest wall in a 7-month-old asymptomatic boy. (a) Anteroposterior radiograph of the chest shows rib deformity and extrapleural soft-tissue mass with faint punctate chondroid mineralization (arrowheads). (b) Sagittal T2-weighted (1,778/80) MR image shows a large fluid level (arrowheads) resulting from hemorrhagic (secondary ABC) components. (c) Photomicrograph corresponds well with imaging findings and reveals hemorrhagic cavities (secondary ABC areas [*]) and chondroid (arrowheads) and osteoid (arrows) regions. (Hematoxylin-eosin stain; original magnification, x200.)

 

fig.ommitted Figure 2b. Mesenchymal hamartoma of the chest wall in a 7-month-old asymptomatic boy. (a) Anteroposterior radiograph of the chest shows rib deformity and extrapleural soft-tissue mass with faint punctate chondroid mineralization (arrowheads). (b) Sagittal T2-weighted (1,778/80) MR image shows a large fluid level (arrowheads) resulting from hemorrhagic (secondary ABC) components. (c) Photomicrograph corresponds well with imaging findings and reveals hemorrhagic cavities (secondary ABC areas [*]) and chondroid (arrowheads) and osteoid (arrows) regions. (Hematoxylin-eosin stain; original magnification, x200.)

 

fig.ommitted Figure 2c. Mesenchymal hamartoma of the chest wall in a 7-month-old asymptomatic boy. (a) Anteroposterior radiograph of the chest shows rib deformity and extrapleural soft-tissue mass with faint punctate chondroid mineralization (arrowheads). (b) Sagittal T2-weighted (1,778/80) MR image shows a large fluid level (arrowheads) resulting from hemorrhagic (secondary ABC) components. (c) Photomicrograph corresponds well with imaging findings and reveals hemorrhagic cavities (secondary ABC areas [*]) and chondroid (arrowheads) and osteoid (arrows) regions. (Hematoxylin-eosin stain; original magnification, x200.)

 
CT scans of all lesions (n = 14) demonstrated a large, heterogeneous, expansile rib lesion, with extrapleural soft-tissue masses containing mineralization, low-attenuating cystic regions, and regions of soft-tissue attenuation (Figs 3, 4). Mineralization was chondroid in appearance in 11 (79%) lesions (Figs 3, 4), osteoid in one (7%) lesion, and mixed osteoid and chondroid in two (14%) lesions (Fig 3). Hemorrhagic cavities (secondary ABC regions) with detectable fluid levels were appreciated in nine (64%) lesions on CT scans (Figs 3, 4). Two patients demonstrated multifocal lesions, one anterior lesion and one posterior lesion affecting the same rib, that were separate and noncontiguous. In both cases, the anterior lesion was less mineralized and less cystic than the posterior lesion (Fig 4). Lung parenchymal hyperaeration was seen in the lung adjacent to the lesion in one case, and a crescent of air surrounded the lesion in another case. In the latter case (Fig 5), it was difficult to determine whether this represented cystic lung disease or pleural air, and the resected specimens did not include adjacent lung.

fig.ommitted Figure 3a. Large mesenchymal hamartoma of the chest wall in a 13-year-old girl with clinical symptoms of periscapular pain and cough. (a) Transverse CT scan shows a large chest wall mass with multiple fluid levels (large arrowheads) resulting from hemorrhagic cavities (secondary ABC regions). Mineralization that appears both osteoid (high-attenuation areas ) and chondroid (punctate regions [small arrowheads]) also is seen. (b) Sectioned gross specimen reveals cystic areas, with (secondary ABC regions [white *]) and without (black *) hemorrhage; chondroid tissue (solid arrow); and osteoid regions (open arrow) that correspond to the CT appearance.

 

fig.ommitted   Figure 3b. Large mesenchymal hamartoma of the chest wall in a 13-year-old girl with clinical symptoms of periscapular pain and cough. (a) Transverse CT scan shows a large chest wall mass with multiple fluid levels (large arrowheads) resulting from hemorrhagic cavities (secondary ABC regions). Mineralization that appears both osteoid (high-attenuation areas ) and chondroid (punctate regions [small arrowheads]) also is seen. (b) Sectioned gross specimen reveals cystic areas, with (secondary ABC regions [white *]) and without (black *) hemorrhage; chondroid tissue (solid arrow); and osteoid regions (open arrow) that correspond to the CT appearance.

 

fig.ommitted   Figure 4a. Multifocal mesenchymal hamartomas manifesting as an anterior chest wall mass in an otherwise asymptomatic 1-day-old girl. (a) Anteroposterior chest radiograph shows a large expansile lesion involving the left seventh and eighth ribs with faint punctate chondroid mineralization (arrowheads). The smaller anterior lesion is not well seen. (b) Transverse CT scan shows the noncontiguous expansile anterior and posterior rib lesions (arrows). Low-attenuating cystic areas (*) with fluid levels resulting from hemorrhagic cavities (secondary ABC areas) and calcification (arrowheads) are more evident in the posterior lesion. (c) Transverse T1-weighted (400/10) MR image reveals fluid levels (arrowheads) and high-signal-intensity foci in the posterior lesion, both resulting from hemorrhage (secondary ABC regions), whereas the anterior lesion is more homogeneous and intermediate in signal intensity.

 

fig.ommitted Figure 4b. Multifocal mesenchymal hamartomas manifesting as an anterior chest wall mass in an otherwise asymptomatic 1-day-old girl. (a) Anteroposterior chest radiograph shows a large expansile lesion involving the left seventh and eighth ribs with faint punctate chondroid mineralization (arrowheads). The smaller anterior lesion is not well seen. (b) Transverse CT scan shows the noncontiguous expansile anterior and posterior rib lesions (arrows). Low-attenuating cystic areas (*) with fluid levels resulting from hemorrhagic cavities (secondary ABC areas) and calcification (arrowheads) are more evident in the posterior lesion. (c) Transverse T1-weighted (400/10) MR image reveals fluid levels (arrowheads) and high-signal-intensity foci in the posterior lesion, both resulting from hemorrhage (secondary ABC regions), whereas the anterior lesion is more homogeneous and intermediate in signal intensity.

 

fig.ommitted Figure 4c. Multifocal mesenchymal hamartomas manifesting as an anterior chest wall mass in an otherwise asymptomatic 1-day-old girl. (a) Anteroposterior chest radiograph shows a large expansile lesion involving the left seventh and eighth ribs with faint punctate chondroid mineralization (arrowheads). The smaller anterior lesion is not well seen. (b) Transverse CT scan shows the noncontiguous expansile anterior and posterior rib lesions (arrows). Low-attenuating cystic areas (*) with fluid levels resulting from hemorrhagic cavities (secondary ABC areas) and calcification (arrowheads) are more evident in the posterior lesion. (c) Transverse T1-weighted (400/10) MR image reveals fluid levels (arrowheads) and high-signal-intensity foci in the posterior lesion, both resulting from hemorrhage (secondary ABC regions), whereas the anterior lesion is more homogeneous and intermediate in signal intensity.

 

fig.ommitted Figure 5. Mesenchymal hamartoma of the chest wall with adjacent lung hyperaeration in a 6-month-old boy with tachypnea and failure to thrive. Transverse CT scan (lung window settings) shows the chest wall mass (*) with crescent of air (arrows) in the surrounding lung parenchyma or pleura.

 
A large expansile rib lesion with an extrapleural soft-tissue mass was seen on MR images in all cases. MR images showed predominantly intermediate and heterogeneous signal intensity on T1-weighted images (n = 9) in all lesions, with seven (78%) of nine lesions also demonstrating areas of focal high signal intensity, reflecting hemorrhagic regions (Figs 1, 4). Four lesions were imaged after intravenous administration of a gadolinium-based contrast agent. All four lesions demonstrated mild to moderate diffuse enhancement of the solid components and lack of enhancement of hemorrhagic and cystic areas (Fig 1). On T2-weighted images (n = 5), all lesions were heterogeneous, with one lesion having predominantly intermediate signal intensity, whereas the other four lesions had primarily high signal intensity (Fig 2). Fluid levels consistent with hemorrhagic cavities (secondary ABC formation) were seen in three (33%) lesions on T1-weighted images (Fig 4) and four (80%) lesions on T2-weighted images (Fig 2). These fluid levels were more obvious on long-TR images.

The diagnosis of mesenchymal hamartoma of the chest wall was confirmed in all patients by means of pathologic review. Gross (Fig 3) and microscopic characteristics of resected specimens corresponded to the cross-sectional imaging features. In all cases, histology revealed mineralized matrix composed of osteoid and prominent chondroid elements, as well as dilated hemorrhagic spaces (secondary ABC regions) with thin walls and septa (Fig 2). No malignant cellular features (nuclear atypia or hyperchromatism) were identified in any lesion.

	DISCUSSION

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Mesenchymal hamartoma of the chest wall is a rare lesion of infancy and childhood. Other names have included mesenchymoma (10–14), infantile osteochondroma (15), and infantile cartilaginous hamartoma (7). The currently accepted name of mesenchymal or chest wall hamartoma, as initially proposed by McLeod and Dahlin in 1979 (1), is now considered the most appropriate, as it best reflects the benign nature and multiple histologic components of this lesion (1,5). Mesenchymal hamartomas are not considered true neoplasms and are composed of maturing, proliferating normal skeletal elements (3,16–18), with no propensity for invasion or metastasis (2).

Mesenchymal hamartomas are well-circumscribed lesions arising from the central portions of ribs, associated with erosion of adjacent ribs at gross examination (12,19). Adjacent structures are compressed by virtue of lesion size, expansion, and extrapleural mass effect (16). However, no invasive characteristics are seen (16). The benign histologic features of the 14 lesions in our study are characteristic of mesenchymal hamartomas of the chest wall. Solid areas composed of a mixture of proliferating maturing elements of bone, cartilage, and fibroblasts, as well as hemorrhagic cystic cavities representing secondary ABC formation, are specific for mesenchymal hamartoma (2,3,17–19). The hypercellular proliferative features may be suggestive of malignancy to pathologists unaware of this lesion, and indeed mesenchymal hamartomas have been misdiagnosed as chondrosarcoma (1,3), osteosarcoma (20), or osteoblastoma (12). These diseases, however, are characterized by aggressive or malignant features, such as nuclear atypia and hyperchromatism, that are notably absent in mesenchymal hamartoma of the chest wall (2,17).

The imaging features of mesenchymal hamartoma of the chest wall reflect the underlying pathologic findings. Radiographic manifestations include a large expansile lesion affecting multiple ribs, with cortical destruction and erosion, and a large extrapleural soft-tissue mass. These radiographic findings suggest a more aggressive process unless one is familiar with mesenchymal hamartoma of the chest wall. Cross-sectional imaging (CT and MR imaging) clearly depicted the rib origin, osseous expansion, and associated extrapleural soft-tissue masses. The intrinsic characteristics corresponded with the pathologic composition of the lesion. CT best demonstrated the matrix mineralization, seen in 100% of lesions in our series, with the mineralization appearing chondroid alone in 79%. Hemorrhagic cystic regions (secondary ABC areas) also were seen with CT (fluid levels in 64% of lesions), although T2-weighted MR images were superior in demonstrating this feature in 80% of cases.

It is interesting that two (17%) of the 12 patients each had two distinct lesions affecting the same rib. In both patients, one lesion was anterior and the other posterior. The lesions also demonstrated similar but not identical imaging features, with the anterior lesion less cystic, less mineralized, and smaller than the posterior lesion. The presence of more than one lesion, although uncommon, has been previously reported (5,12) and constitutes a feature in the spectrum of mesenchymal hamartoma of the chest wall; this feature should not cause confusion with other multifocal disease (metastasis, lymphoma, leukemia).

Accurate diagnosis of mesenchymal hamartoma is important, since many chest wall masses in children are malignant. A majority include the small round cell tumors Ewing sarcoma and primitive neuroectodermal tumor, also known as Askin tumor (16,21,22). Ewing sarcoma or primitive neuroectodermal tumor, the most common primary malignant pediatric rib tumors, usually manifest as a large extrapleural soft-tissue mass and an associated pleural effusion (21). The costal site of origin may be subtle, with rib destruction or even sclerosis. Neuroblastoma, leukemia, and lymphoma are common pediatric tumors that infrequently manifest with chest wall metastases (22). However, none of these malignant tumors frequently affect the chest wall of newborns, nor do they exhibit prominent secondary ABC components. Although chondrosarcoma is the most common primary malignancy of ribs in adults, it is exceedingly rare in children (21). Congenital fibrosarcoma may occur in newborns and must be distinguished from mesenchymal hamartoma, although we are unaware of any cases of congenital fibrosarcoma arising from ribs (16). In contradistinction to malignant tumors, which require surgery, radiation, and/or chemotherapy and are associated with a relatively poor prognosis, mesenchymal hamartomas of the chest wall are typically cured with complete surgical excision. Recurrences have been reported with incomplete resections (2,23). For approximately 60 cases of mesenchymal hamartoma reported at the time this article was written, to our knowledge there is only one report of malignant transformation (23). However, we question the pathologic diagnosis in the patient in that report, who is doing well 6 years after diagnosis of poorly differentiated sarcoma with incomplete resection.

Common benign lesions affecting ribs include fibrous dysplasia, Langerhans cell histiocytosis, and hemangioma. Secondary ABC regions can be associated with fibrous dysplasia and hemangioma. However, the latter are uncommon in newborns and do not show internal mineralization. Thus, in a newborn, a chest wall mass with prominent hemorrhagic cystic (secondary ABC) components and mineralized elements is highly suggestive of mesenchymal hamartoma (2).

Surgical excision of mesenchymal hamartoma of the chest wall is recommended if compressive effects of the mass result in cardiac or pulmonary compromise or if the mass is physically deforming (11,23–25). Small asymptomatic lesions may not require surgical resection (11). Close observation and imaging may represent a more appropriate course of management, since spontaneous lesion regression has been reported (13). Surgical intervention is not without complication, including severe blood loss secondary to the hemorrhagic elements and postoperative scoliosis (11,16). The severity of the scoliosis is directly related to the number of resected ribs and location, with resection of posterior and lower ribs resulting in greater curvature (16). Investigators have described fine-needle aspiration (6), in conjunction with clinical and radiologic features, to accurately diagnose mesenchymal hamartoma and thus avoid open biopsy with its inherent bleeding risks (26–28). However, cytopathologists must be aware of this rare lesion, since its histologic features may suggest sarcoma. One report (26) describes a newborn who died of infection after chemotherapy for a presumed embryonal sarcoma, diagnosed with fine-needle aspiration of a chest wall mass, that ultimately proved to be mesenchymal hamartoma at autopsy.

We recognize certain limitations of our study. Our retrospective review includes only 12 patients with 14 lesions. To our knowledge, however, this is the largest series described to date and includes a greater number of cross-sectional imaging studies than does any previous study. All patients in this series were referral cases, each providing only selected images from different radiologic modalities, without standardization of technical protocols. Despite these limitations, our study describes characteristic cross-sectional imaging features of mesenchymal hamartoma that can facilitate accurate, confident diagnosis and can direct appropriate treatment.

In conclusion, mesenchymal hamartomas of the chest wall are unusual rib lesions most commonly affecting infants. The clinical manifestation and radiographic appearance may suggest a more aggressive malignant process unless one is familiar with this diagnosis. CT and MR imaging findings clearly reflect the underlying histopathologic characteristics of these lesions, demonstrating pathognomonic features of rib origin, mineralized matrix, and hemorrhagic cystic (secondary ABC) components. Accurate diagnosis allows appropriate treatment, which may consist of either close clinical follow-up or surgical resection in symptomatic cases or lesions causing disfiguring chest wall deformity.

　

	ACKNOWLEDGMENTS

 
The authors gratefully thank, from the Department of Radiologic Pathology at the AFIP, Janeth Amarillo for preparation of figures and Chris Buchanan and Linda Wilkins for manuscript preparation. We also thank all past, present, and future attendees of the radiologic pathology course at the AFIP for providing the material that makes such projects possible.

　

	REFERENCES

Top ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. McLeod RA, Dahlin DC. Hamartoma (mesenchymoma) of the chest wall in infancy. Radiology 1979; 131:657-661.

2. Cohen MC, Drut R, Garcia C, Kaschula ROC. Mesenchymal hamartoma of the chest wall: a cooperative study with review of the literature. Pediatr Pathol 1992; 12:525-534.

3. Ayala AG, Ro JY, Bolio-Solis A, Hernandez-Batres F, Eftekhari F, Edeiken J. Mesenchymal hamartoma of the chest wall in infants and children: a clinicopathological study of five patients. Skeletal Radiol 1993; 22:569-576.

4. Jung AL, Johnson DG, Condon VR, Pysher TJ, Reppucci P. Congenital chest wall mesenchymal hamartoma. J Perinatol 1994; 14:487-491.

5. Troum S, Dalton ML, Donner RS, Besser AS. Multifocal mesenchymal hamartoma of the chest wall in infancy. J Pediatr Surg 1996; 31:713-715.

6. Szadowska A, Sitkiewicz A, Jarosik N. Mesenchymal hamartoma of the chest wall in infancy: a case report of this rare entity with cytologic findings. Cytopathology 1996; 7:211-217.

7. Balci P, Obuz F, Gore O, et al. Aneurysmal bone cyst secondary to infantile cartilaginous hamartoma of rib. Pediatr Radiol 1997; 27:767-769.

8. Kim JY, Jung WH, Yoon CS, Kim MJ, Cho SH. Mesenchymal hamartomas of the chest wall in infancy: radiologic and pathologic correlation. Yonsei Med J 2000; 41:615-622.

9. Masuzaki H, Masuzaki M, Ishimaru T, Yamabe T. Chest wall hamartoma diagnosed prenatally using ultrasonography and computed tomography. J Clin Ultrasound 1996; 24:83-85.

10. Schlesinger AE, Smith MB, Genez BM, McMahon DP, Swaney JJ. Chest wall mesenchymoma (hamartoma) in infancy: CT and MR findings. Pediatr Radiol 1989; 19:212-213.

11. Campbell AN, Wagget J, Mott MG. Benign mesenchymoma of the chest wall in infancy. J Surg Oncol 1982; 21:267-270.

12. Oakley RH, Carty H, Cudmore RE. Multiple benign mesenchymomata of the chest wall. Pediatr Radiol 1985; 15:58-60.

13. Blumenthal BI, Capitanio MA, Queloz JM, Kirkpatrick JA. Intrathoracic mesenchymoma. Pediatr Radiol 1972; 104:107-109.

14. Eskelinen M, Veli-Matti K, Vainio J. Mesenchymoma of the chest wall in children. Ann Thorac Surg 1991; 52:291-293.

15. Seibert JJ, Rossi NP, McCarthy EF. A primary rib tumor in a newborn. J Pediatr Surg 1976; 11:1031-1032.

16. Shamberger RC, Grier HE. Chest wall tumors in infants and children. Semin Pediatr Surg 1994; 3:267-276.

17. Odell JM, Benjamin DR. Mesenchymal hamartoma of chest wall in infancy: natural history of two cases. Pediatr Pathol 1986; 5:135-146.

18. Gore O, Kilicalp A, Basdemir G, Ozer E, Aktug T. Cartilaginous hamartoma of the chest wall with secondary aneurysmal cyst-like areas in an infant: a case report. Turk J Pediatr 1999; 41:139-142.

19. McCarthy EF, Dorfman HD. Vascular and cartilaginous hamartoma of the ribs in infancy with secondary aneurysmal bone cyst formation. Am J Surg Pathol 1980; 4:247-253.

20. Hall DP, Ellison RG. Osteochondrosarcoma of the chest wall in a newborn infant: a case report six years after surgery. Am Surg 1964; 30:745-747.

21. Franken EA, Jr, Smith JA, Smith WL. Tumors of the chest wall in infants and children. Pediatr Radiol 1977; 6:13-18.

22. Donnelly LF, Frush DP. Abnormalities of the chest wall in pediatric patients. AJR Am J Roentgenol 1999; 173:1595-1601.

23. Dounies R, Chwals WJ, Lally KP, et al. Hamartomas of the chest wall in infants. Ann Thorac Surg 1994; 57:868-875.

24. Brand T, Hatch EI, Schaller RT, Stevenson JK, Arensman RM, Schwartz MZ. Surgical management of the infant with mesenchymal hamartoma of the chest wall. J Pediatr Surg 1986; 21:556-558.

25. Psaila J, Carachi R, Raine PAM, Patrick WJA. Thoracic mesenchymoma of infancy. J Pediatr Surg 1996; 31:726-728.

26. Castellano VM, Fiano C, Vargas J, de Agustin P. Mesenchymal hamartoma of the chest wall. Cytopathology 1997; 8:210-219.

27. Nicholson SA, Hill DA, Foster KW, McAlister WH, Davila RM, Dehner LP. Fine-needle aspiration cytology of mesenchymal hamartoma of the chest wall. Diagn Cytopathol 2000; 22:33-38.

28. Baretton G, Stehr M, Nerlich A, Loehrs U. Chest wall hamartoma in infancy: a case report with immunohistochemical analysis of various interstitial collagen types. Pediatr Pathol 1994; 14:3-9.